U.S. patent number 7,308,145 [Application Number 10/491,153] was granted by the patent office on 2007-12-11 for moving picture coding method and moving picture decoding method.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Kiyofumi Abe, Makoto Hagai, Shinya Kadono, Satoshi Kondo.
United States Patent |
7,308,145 |
Abe , et al. |
December 11, 2007 |
Moving picture coding method and moving picture decoding method
Abstract
According to a picture coding method of the present invention, a
coded picture identified by a picture number is stored, as a
reference picture, into a storage unit; commands indicating
correspondence between picture numbers and reference indices for
designating reference pictures and coefficients used for generation
of predictive images are generated; a reference picture being used
when motion compensation is performed on a current block in a
current picture to be coded is designated by a reference index; a
predictive image is generated by performing linear prediction on a
block being obtained by motion estimation within the designated
reference picture, by use of a coefficient corresponding to the
reference index; a coded image signal including a coded signal
obtained by coding a prediction error being a difference between
the current block in the current picture to be coded and the
predictive image, the commands, the reference index and the
coefficient is outputted. At that time, information indicating the
maximum reference index value is coded and included into the coded
image signal, and the commands indicating correspondence between at
least one picture number and a plurality of reference indices are
generated.
Inventors: |
Abe; Kiyofumi (Kadoma,
JP), Kadono; Shinya (Nishinomiya, JP),
Kondo; Satoshi (Yawata, JP), Hagai; Makoto
(Moriguchi, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
|
Family
ID: |
31721895 |
Appl.
No.: |
10/491,153 |
Filed: |
July 22, 2003 |
PCT
Filed: |
July 22, 2003 |
PCT No.: |
PCT/JP03/09228 |
371(c)(1),(2),(4) Date: |
March 26, 2004 |
PCT
Pub. No.: |
WO2004/015999 |
PCT
Pub. Date: |
February 19, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050105809 A1 |
May 19, 2005 |
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Foreign Application Priority Data
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Aug 8, 2002 [JP] |
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2002-232160 |
Sep 19, 2002 [JP] |
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2002-273992 |
Oct 1, 2002 [JP] |
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2002-289294 |
Oct 9, 2002 [JP] |
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2002-296726 |
Dec 20, 2002 [JP] |
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2002-370722 |
Jan 16, 2003 [JP] |
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2003-008751 |
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Current U.S.
Class: |
382/233;
375/E7.211; 375/E7.257; 375/E7.262; 375/E7.25; 375/E7.199;
375/E7.093; 375/E7.181; 375/E7.177; 375/E7.129; 375/E7.176;
375/E7.152; 375/E7.133; 375/240.25; 382/236; 382/238; 375/240.27;
375/240.12 |
Current CPC
Class: |
H04N
19/42 (20141101); H04N 19/573 (20141101); H04N
19/134 (20141101); H04N 19/177 (20141101); H04N
19/70 (20141101); H04N 19/46 (20141101); H04N
19/182 (20141101); H04N 19/593 (20141101); H04N
19/61 (20141101); H04N 19/159 (20141101); H04N
19/117 (20141101); H04N 19/18 (20141101); H04N
19/103 (20141101); H04N 19/174 (20141101); H04N
19/139 (20141101); H04N 19/577 (20141101); H04N
19/58 (20141101); H04N 19/172 (20141101); H04N
19/137 (20141101); H04N 19/147 (20141101); H04N
19/176 (20141101); H04N 19/105 (20141101) |
Current International
Class: |
G06T
9/00 (20060101); H04N 7/32 (20060101); H04N
7/64 (20060101) |
Field of
Search: |
;382/232-253 ;348/396.1
;375/240.12,240.25,240.27 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
T Fukuhara, entitled "Very Low Bit-Rate Video Coding With Block
Partitioning and Adaptive Selection of Two Time-Differential Frame
Memories ", IEEE Transactions on Circuits and Systems for Video
Technology, IEEE, Feb. 1997, vol. 7, No. 1, pp. 212-220. cited by
other .
Wiegand, T.: "Text of Final Committee Draft of Joint Video
Specification" (ITU-T Rec. H. 264 / ISO/IEC 14496-10 AVC)
MPEG02/N4920 ISO/IEC JTC1/SC29/WG11 MPEG02/N4920, Klagenfurt, AT,
Jul. 2002, pp. I-XV, 1, XP001100641; pp. III-IV, paragraph 8; pp.
32-42, paragrapn 7.4.2-7.4.3.3; p. 61, paragraph 8.4. cited by
other .
Lim C-S et al.: "Post Decoder Buffer for HRD"; Joint Video Team
(JVT) of ISO/IEC MPEG & ITU-T VCEG (ISO/IEC JTC1/SC29/WG11 and
ITU-T SG16 Q6), No. JVT-D111, Jul. 22, 2002, pp. 1-10, XP002424748;
pp. 3-4, paragraph 3; table A.1. cited by other.
|
Primary Examiner: Rogers; Scott A.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
The invention claimed is:
1. A picture decoding method comprising: decoding a coded image
signal to obtain: a reference index that identifies a reference
picture for a current block to be decoded; commands that indicate
correspondence between reference indices and picture numbers
indicating a decoding order of coded pictures; information that
indicates a maximum reference index value; and a prediction error;
designating, based on the commands and the reference index, a
reference picture which is referred to when the current block is
decoded through motion compensation; generating a weighting
coefficient based on display order information that indicates a
display order of pictures; generating a predictive image by
performing linear prediction, using the weighting coefficient, on
pixel values of a reference block obtained from the reference
picture designated in said designating; and generating a
reconstructed image from the predictive image and the prediction
error, wherein the reference index includes a first reference index
that identifies a first reference picture and a second reference
index that identifies a second reference picture, and in said
generating of the predictive image, the predictive image is
generated by performing linear prediction on the pixel values of
the reference block using a pre-defined weighting coefficient when
the first reference picture identified by the first reference index
and the second reference picture identified by the second reference
index have identical display order information.
2. The picture decoding method according to claim 1, wherein the
pre-defined weighting coefficient for the first reference picture
is identical to the pre-defined weighting coefficient for the
second reference picture.
3. A picture decoding apparatus comprising: a coded image signal
decoding unit operable to decode a coded image signal to obtain: a
reference index that identifies a reference picture for a current
block to be decoded; commands that indicate correspondence between
reference indices and picture numbers indicating a decoding order
of coded pictures; information that indicates a maximum reference
index value; and a prediction error; a reference picture
designating unit operable to designate, based on the commands and
the reference index, a reference picture which is referred to when
the current block is decoded through motion compensation; a
weighting coefficient generating unit operable to generate a
weighting coefficient based on display order information that
indicates a display order of pictures; a predictive image
generating unit operable to generate a predictive image by
performing linear prediction, using the weighting coefficient, on
pixel values of a reference block obtained from the reference
picture designated by said reference picture designating unit; and
a reconstructed image generating unit operable to generate a
reconstructed image from the predictive image and the prediction
error, wherein the reference index includes a first reference index
that identifies a first reference picture and a second reference
index that identifies a second reference picture, and in said
predictive image generating unit, the predictive image is generated
by performing linear prediction on the pixel values of the
reference block using a pre-defined weighting coefficient when the
first reference picture identified by the first reference index and
the second reference picture identified by the second reference
index have identical display order information.
4. A computer-readable data storage medium on which a program for
decoding a coded image signal is stored, wherein the program causes
a computer to perform the decoding by the picture decoding method
according to claim 1.
5. A computer-readable data storage medium on which a program for
decoding a coded image signal is stored, wherein the program causes
a computer to perform the decoding by the picture decoding method
according to claim 2.
Description
TECHNICAL FIELD
The present invention relates to a moving picture coding method and
a moving picture decoding method, and particularly to a coding
method and a decoding method using inter-picture prediction with
reference to previously coded pictures.
BACKGROUND ART
With the development of multimedia applications, it has become
popular to handle integrally all kinds of media information such as
video, audio and text. For that purpose, digitalization of all
these kinds of media allows handling of them in an integral manner.
However, since digitized images have an enormous amount of data,
image information compression techniques are absolutely essential
for storage and transmission of such information. It is also
important to standardize such compression techniques for
interoperation of compressed image data. There exist international
standards for image compression techniques, such as H.261 and H.263
standardized by International Telecommunication Union -
Telecommunication Standardization Sector (ITU-T) and MPEG-1, MPEG-4
and others standardized by International Organization for
Standardization (ISO). ITU is now working for standardization of
H.26L as the latest standard for image coding.
In coding of moving pictures, in general, information amount is
compressed by reducing redundancies in both temporal and spatial
directions. Therefore, in inter-picture prediction coding, which
aims at reducing the temporal redundancy, motion of a current
picture is estimated on a block-by-block basis with reference to
preceding or subsequent pictures so as to create a predictive
image, and then differential values between the obtained predictive
images and the current picture are coded.
Here, the term "picture" represents a single sheet of an image, and
it represents a frame when used in a context of a progressive
image, whereas it represents a frame or a field in a context of an
interlaced image. The interlaced image here is a single frame that
is made up of two fields having different times respectively. In
the process of coding and decoding the interlaced image, a single
frame can be handled as a frame, as two fields, or as a frame
structure or a field structure on every block in the frame.
The following description will be given assuming that a picture is
a frame in a progressive image, but the same description can be
given even assuming that a picture is a frame or a field in an
interlaced image.
FIG. 30 is a diagram for explaining types of pictures and reference
relations between them.
A picture like a picture I1, which is intra-picture prediction
coded without reference to any pictures, is referred to as an
I-picture. A picture like a picture P10, which is inter-picture
prediction coded with reference to only one picture, is referred to
as a P-picture. And a picture, which can be inter-picture
prediction coded with reference to two pictures at the same time,
is referred to as a B-picture.
B-pictures, like pictures B6, B12 and B18, can refer to two
pictures located in arbitrary temporal directions. Reference
pictures can be designated on a block-by-block basis, on which
motion is estimated, and they are discriminated between a first
reference picture which is described earlier in a coded stream
obtained by coding pictures and a second reference picture which is
described later in the coded stream.
However, it is required in order to code and decode the above
pictures that the reference pictures be already coded and decoded.
FIGS. 31A and 31B show examples of order of coding and decoding
B-pictures. FIG. 31A shows a display order of the pictures, and
FIG. 31B shows a coding and decoding order reordered from the
display order as shown in FIG. 31A. These diagrams show that the
pictures are reordered so that the pictures which are referred to
by the pictures B3 and B6 are previously coded and decoded.
A method for creating a predictive image in the case where the
above-mentioned B-picture is coded with reference to two pictures
at the same time will be explained in detail using FIG. 32. Note
that a predictive image is created in decoding in exactly the same
manner.
The picture B4 is a current B-picture to be coded, and blocks BL01
and BL02 are current blocks to be coded belonging to the current
B-picture. Referring to a block BL11 belonging to the picture P2 as
a first reference picture and BL21 belonging to the picture P3 as a
second reference picture, a predictive image for the block BL01 is
created. Similarly, referring to a block BL12 belonging to the
picture P2 as a first reference picture and a block BL22 belonging
to the picture P1 as a second reference picture, a predictive image
for the block BL02 is created (See Non-patent document 1).
FIG. 33 is a diagram for explaining a method for creating a
predictive image for the current block to be coded BL01 using the
referred two blocks BL11 and BL21. The following explanation is
made assuming here that a size of each block is 4 by 4 pixels.
Assuming that Q1(i) is a pixel value of BL11, Q2(i) is a pixel
value of BL21 and P(i) is a pixel value of the predictive image for
the target BL01, the pixel value P(i) can be calculated by a linear
prediction equation like the following equation 1. "i" indicates
the position of a pixel, and in this example, "i" has values of 0
to 15. P(i)=(w1.times.Q1(i)+w2.times.Q2(i))/pow(2, d)+c Equation 1
(where pow(2, d) indicates the "d"th power of 2) "w1", "w2", "c"
and "d" are coefficients for performing linear prediction, and
these four coefficients are handled as one set of weighting
coefficients. This weighting coefficient set is determined by a
reference index designating a picture referred to by each block.
For example, four values of w1.sub.--1, w2.sub.--1, c.sub.--1 and
d.sub.--1 are used for BL01, and w1.sub.--2, w2.sub.--2, c.sub.--2
and d.sub.--2 are used for BL02, respectively.
Next, reference indices designating reference pictures will be
explained with reference to FIG. 34 and FIG. 35. A value referred
to as a picture number, which increases one by one every time a
picture is stored in a memory, is assigned to each picture. In
other words, a picture number with a value added one to the maximum
value of the existing picture numbers is assigned to a newly stored
picture. However, a reference picture is not actually designated
using this picture number, but using a value referred to as a
reference index which is defined separately. Indices indicating
first reference pictures are referred to as first reference
indices, and indices indicating second reference pictures are
referred to as second reference indices, respectively.
FIG. 34 is a diagram for explaining a method for assigning two
reference indices to picture numbers. When there is a sequence of
pictures ordered in display order, picture numbers are assigned in
coding order. Commands for assigning the reference indices to the
picture numbers are described in a header of a slice that is a
subdivision of a picture, as the unit of coding, and thus the
assignment thereof are updated every time one slice is coded. The
command indicates the differential value between a picture number
assigned a reference index currently and a picture number assigned
a reference index immediately before the current assignment, in
series by the number of reference indices.
Taking the first reference index in FIG. 34 as an example, since
"-1" is given as a command first, 1 is subtracted from the picture
number 16 of the current picture to be coded and thus the reference
index 0 is assigned to the picture number 15. Next, since "-4" is
given, 4 is subtracted from the picture number 15 and thus the
reference index 1 is assigned to the picture number 11. The
following reference indices are assigned to respective picture
numbers in the same processing. The same goes for the second
reference indices.
FIG. 35 shows the result of the assignment of the reference
indices. The first reference indices and the second reference
indices are assigned to respective picture numbers separately, but
focusing attention to each reference index, it is obvious that one
reference index is assigned to one picture number.
Next, a method for determining weighting coefficient sets to be
used will be explained with reference to FIG. 36 and FIG. 37.
A coded stream of one picture is made up of a picture common
information area and a plurality of slice data areas. FIG. 36 shows
a structure of one slice data area among them. The slice data area
is made up of a slice header area and a plurality of block data
areas. As one example of a block data area, block areas
corresponding to BL01 and BL02 in FIG. 32 are shown here.
"ref1" and "ref2" included in the block BL01 indicate the first
reference index and the second index indicating two reference
pictures for this block, respectively. In the slice header area,
data (pset0, pset1, pset2, pset3 and pset4) for determining the
weighting coefficient sets for the linear prediction are described
for ref1 and ref2, respectively. FIG. 37 shows tables of the
above-mentioned data included in the slice header area as an
example.
Each data indicated by an identifier "pset" has four values, w1,
w25, c and d, and is structured so as to be directly referred to by
the values of ref1 and ref2. Also, in the slice header area, a
command sequence idx_cmd1 and idx_cmd2 for assigning the reference
indices to the picture numbers are described.
Using ref1 and ref2 described in BL01 in FIG. 36, one set of
weighting coefficients is selected from the table for ref1 and
another set of them is selected from the table for ref2. By
performing linear prediction of the equation 1 using respective
weighting coefficient sets, two predictive images are generated. A
desired predictive image can be obtained by averaging these two
predictive images on a per-pixel basis.
In addition, there is a method for obtaining a predictive image
using a predetermined fixed equation, unlike the above-mentioned
method for generating a predictive image using a prediction
equation obtained by weighting coefficient sets of linear
prediction coefficients. In the former method, in the case where a
picture designated by a first reference index appears later in
display order than a picture designated by a second reference
index, the following equation 2a being a fixed equation composed of
fixed coefficients is selected, and in other cases, the following
equation 2b being a fixed equation composed of fixed coefficients
is selected, so as to generate a predictive image.
P(i)=2.times.Q1(i)-Q2(i) Equation 2a P(i)=(Q1(i)+Q2(i))/2 Equation
2b
As is obvious from the above, this method has the advantage that
there is no need to code and transmit the weighting coefficient
sets to obtain the predictive image because the prediction equation
is fixed. This method has another advantage that there is no need
to code and transmit a flag for designating the weighting
coefficient sets of linear prediction coefficients because the
fixed equation is selected based on the positional relationship
between pictures. In addition, this method allows significant
reduction of an amount of processing for linear prediction because
of a simple formula for linear prediction.
(Nonpatent document 1)
ITU-T Rec. H.264 |ISO/IEC 14496-10 AVC
Joint Committee Draft (CD)
(2002-5-10)
(P.34 8.4.3 Re-Mapping of frame numbers indicator,
P.105 11.5 Prediction signal generation procedure)
In the method for creating a predictive image using weighting
coefficient sets based on the equation 1, since the number of
commands for assigning reference indices to reference pictures is
same as the number of the reference pictures, only one reference
index is assigned to one reference picture, and thus the weighting
coefficient sets used for linear prediction of the blocks referring
to the same reference picture have exactly the same values. There
is no problem if images change uniformly in a picture as a whole,
but there is a high possibility that the optimum predictive image
cannot be generated if respective images change differently. In
addition, there is another problem that the amount of processing
for linear prediction increases because the equation includes
multiplications.
SUMMARY OF THE INVENTION
Against this backdrop, it is an object of the present invention to
provide a picture coding method and a picture decoding method and
apparatuses and programs for executing these methods for allowing
assignment of a plurality of reference indices to one reference
picture and thus improving decoding efficiency of reference indices
in both cases where a plurality of reference indices are assigned
and one reference index is assigned.
In order to achieve this object, the picture coding method
according to the present invention is structured as follows. The
picture coding method according to the present invention includes:
a reference picture storage step of storing a coded picture
identified by a picture number, as a reference picture, into a
storage unit; a command generation step of generating commands
indicating correspondence between reference indices and picture
numbers, said reference indices designating reference pictures and
coefficients used for generation of predictive images; a reference
picture designation step of designating a reference picture by a
reference index, said reference picture being used when motion
compensation is performed on a current block in a current picture
to be coded; a predictive image generation step of generating a
predictive image by performing linear prediction on a block by use
of a coefficient corresponding to the reference index, said block
being obtained by motion estimation within the reference picture
designated in the reference picture designation step; and a coded
signal output step of outputting a coded image signal including a
coded signal obtained by coding a prediction error, the commands,
the reference index and the coefficient, said prediction error
being a difference between the current block in the current picture
to be coded and the predictive image, wherein in the coded signal
output step, information indicating a maximum reference index value
is coded and placed into the coded image signal.
Here, it may be structured so that the information indicating the
maximum reference index value is placed in a picture common
information area included in the coded image signal.
According to this structure, when picture numbers and reference
indices are corresponded to each other according to the commands in
the decoding apparatus, information indicating the maximum
reference index value is included in the coded signal. Therefore,
by corresponding the picture numbers and the reference indices
according to the commands until the number of reference indices
reaches the maximum value, all the reference indices and the
pictures numbers can be corresponded to each other easily. As a
result, it is possible not only to assign a plurality of reference
indices to one reference picture, but also to perform decoding of
the reference indices efficiently in either case where a plurality
of reference indices are assigned or one reference index is
assigned.
Here, it may be structured so that in the command generation step,
the commands are generated so that at least one reference picture,
among reference pictures stored in the storage unit, has a picture
number assigned a plurality of reference indices.
Also, it may be structured so that in the reference picture
designation step, when the plurality of reference indices are
corresponded to the picture number of the reference picture, one of
the reference indices is selected based on coefficients
corresponding respectively to said plurality of reference indices,
and in the predictive image generation step, the linear prediction
is performed using a coefficient corresponding to the reference
index selected in the reference picture designation step.
According to this structure, a plurality of reference indices are
corresponded to one picture. Therefore, when linear prediction is
performed using the coefficient corresponding to the reference
index designating the reference picture, that coefficient can be
selected from among a plurality of coefficients. In other words,
the optimum coefficient can be selected as a coefficient used for
the linear prediction. As a result, the coding efficiency can be
improved.
Here, it may be structured so that in the predictive image
generation step, the linear prediction is performed using only a
bit shift operation, an addition and a subtraction.
According to this structure, multiplications and divisions which
require heavy processing load are not used, but only bit shift
operations, additions and subtractions which require smaller
processing load are used, so the processing amount of linear
prediction can be reduced.
Here, it may be structured so that in the predictive image
generation step, as the coefficient used in the linear prediction,
only a value indicating a direct current component in a linear
prediction equation is corresponded to the reference index.
According to this structure, values of coefficients other than the
value indicating a DC component do not need to be coded, so the
coding efficiency can be improved. Also, since multiplications and
divisions which require heavy processing load are not used but
additions and subtractions which require smaller processing load
are used, the processing amount for linear prediction can be
restrained.
Here, it may be structured so that the reference index has a first
reference index indicating a first reference picture and a second
reference index indicating a second reference picture, and in the
predictive image generation step, in the case where a method for
generating the coefficient according to display order information
of each of the reference pictures is used as a method for
performing the linear prediction, when a reference picture
designated by the first reference index and a reference picture
designated by the second reference index have the same display
order information, the linear prediction is performed using a
predetermined coefficient for each of the first and second
reference indices instead of the coefficient.
Also, it may be structured so that the predetermined coefficients
have the same weight.
According to this structure, it is possible to determine the
coefficients for performing linear prediction even in the case
where two reference pictures have the same display order
information, and thus the coding efficiency can be improved.
Also, the picture decoding method, the picture coding apparatus,
the picture decoding apparatus, the picture coding program, the
picture decoding program, and the coded picture data of the present
invention have the same structures, functions and effects as the
picture coding method described above.
In addition, the picture coding method of the present invention can
be structured in any of the following manners (1) to (14).
(1) The picture coding method according to the present invention
includes: a reference picture storage step of storing a coded
picture identified by a picture number into a storage unit; a
command generation step of generating commands for allowing a
plurality of reference indices to refer to the same picture, said
commands indicating correspondence between reference indices and
picture numbers, said reference indices designating reference
pictures and coefficients used for generation of predictive images,
and said reference pictures being referred to when motion
compensation is performed on a current block in a current picture
to be coded and selected arbitrarily from among a plurality of
coded pictures stored in the storage unit; a reference picture
designation step of designating a reference picture by a reference
index, said reference picture being referred to when motion
compensation is performed on the current block in the current
picture to be coded; a predictive image generation step of
generating a predictive image by performing linear prediction on a
block by use of a coefficient corresponding to the reference index
designating the reference picture, said block being obtained by
motion estimation on the reference picture designated in the
reference picture designation step; and a coded signal output step
of outputting a coded image signal including a coded signal
obtained by coding a prediction error, the commands, the reference
index and the coefficient, said prediction error being a difference
between the current block in the current frame to be coded and the
predictive image.
(2) According to another picture coding method of the present
invention, it is possible to assign a plurality of reference
indices to the picture number of the reference picture, and it is
also possible to select one reference index from among one or more
reference indices corresponding to respective coded pictures in the
reference picture designation step and thus determine the
coefficient used for linear prediction in the predictive image
generation step.
(3) According to another picture coding method of the present
invention, at least one reference picture, among a plurality of
reference pictures referred to by one slice, has a picture number
assigned a plurality of reference indices.
(4) According to another picture coding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among the plurality of coded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among the plurality of coded frames,
wherein in the predictive image generation step, the linear
prediction is performed on the block by a coefficient corresponding
to the first reference index, and the linear prediction is
performed on the block by a coefficient corresponding to the second
reference index, and then a final predictive image for the block is
generated by calculating an average of pixel values in the two
predictive images respectively obtained by the linear
predictions.
(5) According to another picture coding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among the plurality of coded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among the plurality of coded frames,
wherein in the predictive image generation step, the coefficient
used for the linear prediction is determined by calculating an
average of the coefficients designated by the selected first
reference index and the selected second reference index
respectively.
(6) According to another picture coding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among the plurality of coded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among the plurality of coded frames,
wherein sets of coefficients are corresponded to the first
reference index and the second reference index, and in the
predictive image generation step, the predictive image is generated
using a part of the coefficient set corresponding to one of the
first and second reference indices and a part of the coefficient
set corresponding to the other reference index.
(7) According to another picture coding method of the present
invention, in an equation used for the linear prediction in the
predictive image generation step, neither a multiplication nor a
division are used but only a bit shift operation, an addition and a
subtraction are used. Accordingly, the linear prediction can be
realized by performing the processing with a smaller amount of
calculations.
(8) According to another picture coding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among the plurality of coded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among the plurality of coded frames,
wherein in the predictive image generation step, the predictive
image is generated using the coefficient corresponding to either
one of the first reference index and the second reference index
which is selected, as a coefficient used for the bit shift
operation, from among the coefficient sets corresponding to the
first reference index and the second reference index, and using an
average of the coefficients corresponding to the first reference
index and the second reference index respectively as a coefficient
used for other operations.
(9) According to another picture coding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among the plurality of coded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among the plurality of coded frames,
wherein in the predictive image generation step, only a value
indicating a direct current component in a linear prediction
equation is used as a coefficient used for the linear prediction,
and one coefficient is corresponded to each of the first reference
index and the second reference index.
(10) Another picture coding method of the present invention
includes: a reference picture storage step of storing a coded
picture identified by a picture number into a storage unit; a
command generation step of generating commands for allowing a
plurality of reference indices to refer to the same picture, said
commands indicating correspondence between reference indices and
picture numbers, said reference indices indicating reference
pictures which are referred to when motion compensation is
performed on a current block in a current picture to be coded and
selected arbitrarily from among a plurality of coded pictures
stored in the storage unit; a reference picture designation step of
designating a reference picture by a reference index, said
reference picture being referred to when motion compensation is
performed on the current block in the current picture to be coded;
a predictive image generation step of generating a coefficient from
display order information of each reference picture and generating
a predictive image by performing linear prediction on a block by
use of the generated coefficient, said block being obtained by
motion estimation on the reference picture designated in the
reference picture designation step; and a coded signal output step
of outputting a coded image signal including a coded signal
obtained by coding a prediction error, the commands, the reference
index and the coefficient, said prediction error being a difference
between the current block in the current frame to be coded and the
predictive image.
(11) According to another picture coding method of the present
invention, in the predictive image generation step, as a method for
performing the linear prediction, a method using the coefficient
generated according to the display order information and a method
using a predetermined fixed equation are switched for use based on
the display order information indicating temporal relationship
between the reference picture designated by the first reference
index and the reference picture designated by the second reference
index.
(12) According to another picture coding method of the present
invention, in the predictive image generation step, in the case
where a method using the coefficient generated according to display
order information of each of the reference pictures is used as a
method for performing the linear prediction, when a reference
picture designated by the first reference index and a reference
picture designated by the second reference index have the same
display order information, the linear prediction is performed using
a predetermined coefficient for each of the first and second
reference indices instead of the coefficient.
(13) According to another picture coding method of the present
invention, in the predictive image generation step, when the
coefficient is generated using the display order information, the
coefficient is approximated to a power of 2 so that the linear
prediction can be performed not using a multiplication nor a
division but using only a bit shift operation, an addition and a
subtraction.
(14) According to another picture coding method of the present
invention, when the approximation is performed, a round-up
approximation and a round-down approximation are switched for use
based on the display order information indicating temporal
relationship between the reference picture designated.by the first
reference index and the reference picture designated by the second
reference index.
(15) A program of the present invention may be structured so as to
cause a computer to execute the picture coding method described in
any of the above-mentioned (1) to (14).
Furthermore, a computer readable recording medium of the present
invention may be structured as described in the following (16) to
(25).
(16) A computer readable recording medium on which a coded signal
that is a signal of a coded moving picture is recorded, wherein the
coded signal including data obtained by coding the following: a
coefficient used for generation of a predictive image; commands for
allowing a plurality of reference indices to refer to the same
picture, said commands indicating correspondence between reference
indices and picture numbers, said reference indices designating
reference pictures and coefficients used for generation of
predictive images, and said reference pictures being referred to
when motion compensation is performed on a current block in a
current picture to be coded and selected arbitrarily from among a
plurality of coded pictures stored in a storage unit for storing
the coded pictures identified by the picture numbers; a reference
index for designating the coefficient used for generation of the
predictive image and the reference picture used when motion
compensation is performed on the current block in the current
picture; the predictive image which is generated by performing
linear prediction on a block by use of the coefficient
corresponding to the reference index designating the reference
picture, said block being obtained by motion estimation on the
selected reference picture.
(17) The coded signal includes the maximum reference index
value.
(18) The maximum value is placed in a picture common information
area included in the coded signal.
(19) A header of a slice including a plurality of blocks, a picture
common information area, or a header of each block, which is
included in the coded signal, includes a flag indicating whether a
coefficient used for generating a predictive image of the block
using linear prediction has been coded or not.
(20) A header of a slice including a plurality of blocks, a picture
common information area, or a header of each block, which is
included in the coded signal, includes a flag indicating whether to
generate the predictive image of the block not using a coefficient
but using a predetermined fixed equation or to generate the
predictive image using a predetermined fixed equation by use of
only a coefficient indicating a direct current component.
(21) A header of a slice including a plurality of blocks, a picture
common information area, or a header of each block, which is
included in the coded signal, includes a flag indicating whether to
generate the predictive image of the block using two predetermined
equations by switching between them or to generate the predictive
image using either one of the two equations, when the predictive
image is generated using a fixed equation that consists of the two
equations.
(22) A header of a slice including a plurality of blocks, a picture
common information area, or a header of each block, which is
included in the coded signal, includes a flag indicating whether or
not to generate a coefficient used for generating the predictive
image of the block by linear prediction using display order
information of a reference picture.
(23) A header of a slice including a plurality of blocks, a picture
common information area, or a header of each block, which is
included in the coded signal, includes a flag indicating whether or
not to approximate a coefficient used for generating the predictive
image of the block by linear prediction to a power of 2.
(24) The coded signal includes a flag indicating that calculation
for the linear prediction can be carried out not using a
multiplication nor a division but using only a bit shift operation,
an addition and a subtraction.
(25) The coded signal includes a flag indicating that calculation
for the linear prediction can be carried out using only a value
indicating a direct current component.
Furthermore, the picture decoding method of the present invention
can be structured as described in the following (26) to (39).
(26) The picture decoding method of the present invention includes:
a coded image information obtainment step for decoding a coded
image signal including a coded signal obtained by coding
coefficients used for generation of predictive images, commands for
allowing a plurality of reference indices to refer to the same
picture, reference indices and a prediction error, said commands
indicating correspondence between the reference indices and picture
numbers, said reference indices designating reference pictures and
the coefficients, and said reference pictures being referred to
when motion compensation is performed on a current block in a
current picture to be coded and selected arbitrarily from among a
plurality of coded pictures stored in a storage unit; a reference
picture designation step of designating a reference picture
according to decoded commands and a decoded reference index, said
reference picture being used when motion compensation is performed
on a current block in a current picture to be decoded; a predictive
image generation step of generating a predictive image by
performing linear prediction on a block by use of a coefficient
corresponding to the reference index designating the reference
picture, said block being obtained by motion estimation on the
designated reference picture; and a decoded image generation step
of generating a decoded image from the predictive image and a
decoded prediction error.
(27) According to another picture decoding method of the present
invention, it is possible to assign a plurality of reference
indices to the picture number of the reference picture, and
determine the coefficient used for linear prediction in the
predictive image generation step using the reference index decoded
in the reference picture designation step.
(28) According to another picture decoding method of the present
invention, at least one reference picture, among a plurality of
reference pictures referred to by one slice, has a picture number
assigned a plurality of reference indices.
(29) According to another picture decoding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among a plurality of decoded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among a plurality of decoded frames,
wherein in the predictive image generation step, the linear
prediction is performed on the block by a coefficient corresponding
to the first reference index, and the linear prediction is
performed on the block by a coefficient corresponding to the second
reference index, and then a final predictive image for the block is
generated by calculating an average of pixel values in the two
predictive images respectively obtained by the linear
prediction.
(30) According to another picture decoding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated by a plurality of decoded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among a plurality of decoded frames,
wherein in the predictive image generation step, the coefficient
used for the linear prediction is determined by calculating an
average of the coefficients designated by the selected first
reference index and the selected second reference index
respectively.
(31) According to another picture decoding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among a plurality of decoded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among a plurality of decoded frames,
wherein sets of coefficients are corresponded to the first
reference index and the second reference index, and in the
predictive image generation step, the predictive image is generated
using a part of the coefficient set corresponding to one of the
first and second reference indices and a part of the coefficient
set corresponding to the other reference index.
(32) According to another picture decoding method of the present
invention, in an equation used for the linear prediction in the
predictive image generation step, neither a multiplication nor a
division are not used but only a bit shift operation, an addition
and a subtraction are used. Accordingly, the linear prediction can
be realized by performing the processing with smaller amount of
calculations.
(33) According to another picture decoding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among a plurality of decoded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among a plurality of decoded frames,
wherein in the predictive image generation step, a predictive image
is generated using the coefficient corresponding to either one of
the first reference index and the second reference index which is
selected, as a coefficient used for the bit shift operation, from
among the coefficient sets corresponding to the first reference
index and the second reference index, and using an average of the
coefficients corresponding to the first reference index and the
second reference index respectively as a coefficient used for other
operations.
(34) According to another picture decoding method of the present
invention, the reference index includes a first reference index
indicating a first reference picture which is arbitrarily
designated from among a plurality of decoded pictures and a second
reference index indicating a second reference frame which is
arbitrarily designated from among a plurality of decoded frames,
wherein in the predictive image generation step, only a value
indicating a direct current component in a linear prediction
equation is used as a coefficient used for the linear prediction,
and one coefficient is corresponded to each of the first reference
index and the second reference index.
(35) The picture decoding method of the present invention includes:
a first step for decoding a coded image signal including a coded
signal obtained by coding commands for allowing a plurality of
reference indices to refer to the same picture, reference indices
and a prediction error, said commands indicating correspondence
between the reference indices and picture numbers, said reference
indices designating reference pictures which are referred to when
motion compensation is performed on a current block in a current
picture to be coded and selected arbitrarily from among a plurality
of coded pictures stored in a storage unit; a reference picture
designation step of designating a reference picture according to
decoded commands and a decoded reference index, said reference
picture being used when motion compensation is performed on a
current block in a current picture to be decoded; a predictive
image generation step of generating a coefficient from display
order information of each reference picture and generating a
predictive image by performing linear prediction on a block by use
of the generated coefficient, said block being obtained by motion
estimation on the designated reference picture; and a decoded image
generation step of generating a decoded image from the predictive
image and a decoded prediction error.
(36) In the predictive image generation step, as a method for
performing the linear prediction, a method using a coefficient
generated according to the display order information and a method
using a predetermined fixed equation are switched for use based on
the display order information indicating temporal relationship
between the reference picture designated by the first reference
index and the reference picture designated by the second reference
index.
(37) According to another picture decoding method of the present
invention, in the predictive image generation step, in the case
where a method using the coefficient generated according to display
order information of each of the reference pictures is used as a
method for performing the linear prediction, when a reference
picture designated by the first reference index and a reference
picture designated by the second reference index have the same
display order information, the linear prediction is performed using
a predetermined coefficient for each of the first and second
reference indices instead of the coefficient.
(38) According to another picture decoding method of the present
invention, in the predictive image generation step, when the
coefficient is generated using the display order information, the
coefficient is approximated to a power of 2 so that the linear
prediction can be performed not using a multiplication nor a
division but using a bit shift operation, an addition and a
subtraction.
(39) According to another picture decoding method of the present
invention, when the approximation is performed, a round-up
approximation and a round-down approximation are switched for use
based on the display order information indicating temporal
relationship between the reference picture designated by the first
reference index and the reference picture designated by the second
reference index.
(40) A program of the present invention may be structured so as to
cause a computer to execute the picture decoding method described
in any of the above-mentioned (26) to (39).
As described above, the moving picture coding method and the moving
picture decoding method of the present invention allow creation of
a plurality of candidates for weighting coefficient sets used in
linear prediction for generating a predictive image, and thus allow
selection of the optimum set for each block. As a result, the
reference indices can be decoded more efficiently in either case
where a plurality of reference indices are assigned or one
reference index is assigned. In addition, since the present
invention allows significant improvement of coding efficiency, it
is very effective for coding and decoding of moving pictures.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram showing a structure of a coding apparatus
in a first embodiment of the present invention.
FIG. 2 is a block diagram showing a structure of a decoding
apparatus in a sixth embodiment of the present invention.
FIG. 3 is a schematic diagram for explaining a method for assigning
reference indices to picture numbers.
FIG. 4 is a schematic diagram showing an example of relationship
between reference indices and picture numbers.
FIG. 5 is a schematic diagram for explaining operations for motion
compensation.
FIG. 6 is a schematic diagram for explaining a structure of a coded
stream.
FIG. 7 is a schematic diagram showing an example of weighting
coefficient sets of linear prediction coefficients.
FIG. 8 is a functional block diagram showing generation of a
predictive image in a coding apparatus.
FIG. 9 is another functional block diagram showing generation of a
predictive image in the coding apparatus.
FIGS. 10A and 10B are still other functional block diagrams showing
generation of a predictive image in the coding apparatus.
FIG. 11 is still another functional block diagram showing
generation of a predictive image in the coding apparatus.
FIG. 12 is a schematic diagram for explaining a structure of a
coded stream.
FIG. 13 is a schematic diagram showing an example of weighting
coefficient sets of linear prediction coefficients.
FIG. 14 is a schematic diagram for explaining a structure of a
coded stream.
FIG. 15 is a schematic diagram showing an example of weighting
coefficient sets of linear prediction coefficients.
FIG. 16 is a functional block diagram showing generation of a
predictive image in the coding apparatus.
FIGS. 17A and 17B are schematic diagrams for explaining a structure
of a coded stream and an example of flags.
FIG. 18 is a functional block diagram showing generation of a
predictive image in a decoding apparatus.
FIG. 19 is another functional block diagram showing generation of a
predictive image in the decoding apparatus.
FIGS. 20A and 20B are still other functional block diagrams showing
generation of a predictive image in the decoding apparatus.
FIG. 21 is still another functional block diagram showing
generation of a predictive image in the decoding apparatus.
FIG. 22 is still another functional block diagram showing
generation of a predictive image in the decoding apparatus.
FIG. 23 is a schematic diagram for explaining a structure of a
coded stream.
FIG. 24 is a schematic diagram for explaining a structure of a
coded stream.
FIGS. 25A, B and C are illustrations of a recording medium for
storing a program for realizing the moving picture coding method
and moving picture decoding method in each of the above-mentioned
embodiments using a computer system.
FIG. 26 is a block diagram showing an overall configuration of a
content supply system.
FIG. 27 is an external view of a mobile phone.
FIG. 28 is a block diagram showing a structure of the mobile
phone.
FIG. 29 is a diagram showing an example of a digital broadcasting
system.
FIG. 30 is a schematic diagram for explaining reference relations
between pictures in a background art.
FIGS. 31A and B are schematic diagrams for explaining reordering of
pictures in the background art.
FIG. 32 is a schematic diagram for explaining operations for motion
compensation in the background art.
FIG. 33 is a schematic diagram for explaining operations for linear
prediction processing in the background art.
FIG. 34 is a schematic diagram for explaining a method for
assigning reference indices to picture numbers in the background
art.
FIG. 35 is a schematic diagram showing an example of relationship
between reference indices and picture numbers in the background
art.
FIG. 36 is a schematic diagram for explaining a structure of a
coded stream in the background art.
FIG. 37 is a schematic diagram showing an example of weighting
coefficient sets of linear prediction coefficients in the
background art.
FIG. 38 is a schematic diagram for explaining a structure of a
coded stream in the background art.
FIG. 39 is a schematic diagram for explaining relationship between
picture numbers and display order information.
FIGS. 40A and 40B are schematic diagrams for explaining a structure
of a coded stream and an example of flags.
FIGS. 41A and 41B are schematic diagrams for explaining a structure
of a coded stream and an example of flags.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
FIG. 1 is a block diagram showing a structure of a moving picture
coding apparatus in the first embodiment of the present invention.
The moving picture coding method executed in this moving picture
coding apparatus, specifically, (1) an overview of coding, (2) a
method for assigning reference indices and (3) a method for
generating a predictive image, will be explained in this order
using the block diagram as shown in FIG. 1.
(1) Overview of Coding
A moving picture to be coded is inputted to a picture memory 101 on
a picture-by-picture basis in display order, and the inputted
pictures are reordered into coding order. FIGS. 31A and 31B are
diagrams showing an example of reordering of pictures. FIG. 31A
shows an example of pictures in display order, and FIG. 31B shows
an example of the pictures reordered into coding order. Here, since
pictures B3 and B6 refer both temporally preceding and subsequent
pictures, the reference pictures need to be coded before coding
these current pictures and thus the pictures are reordered in FIG.
31B so that pictures P4 and P7 are coded earlier. Each of the
pictures is divided into blocks, each of which is called a
macroblock of horizontal 16 by vertical 16 pixels, for example, and
the following proceeding is performed on a block-by-block
basis.
An input image signal read out from the picture memory 101 is
inputted to a difference calculation unit 112. The difference
calculation unit 112 calculates a difference between the input
image signal and the predictive image signal outputted from a
motion compensation coding unit 107, and outputs the obtained
difference image signal (prediction error signal) to a prediction
error coding unit 102. The prediction error coding unit 102
performs image coding processing such as frequency transformation
and quantization, and outputs a coded error signal. The coded error
signal is inputted to a prediction error decoding unit 104, which
performs image decoding processing such as inverse-quantization and
inverse-frequency transformation, and outputs a decoded error
signal. An addition unit 113 adds the decoded error signal and the
predictive image signal to generate a reconstructed image signal,
and stores, into a picture memory 105, the reconstructed image
signals which could be referred in the following inter-picture
prediction out of the obtained reconstructed image signals.
On the other hand, the input image signal read out per macroblock
from the picture memory 101 is also inputted into a motion vector
estimation unit 106. Here, the reconstructed image signals stored
in the picture memory 105 are searched so as to estimate an image
area which is the most alike to the input image signal and thus
determine a motion vector pointing to the position of the image
area. The motion vector estimation is performed per block that is a
subdivision of a macroblock, and the obtained motion vectors are
stored in a motion vector storage unit 108.
At this time, since a plurality of pictures can be used for
reference in H.26L which is now under consideration for
standardization, identification numbers for designating reference
pictures are needed per block. The identification numbers are
referred to as reference indices, and a reference index/picture
number conversion unit 111 establishes correspondence between the
reference indices and the picture numbers of the pictures stored in
the picture memory 105 so as to allow designation of the reference
pictures. The operation in the reference index/picture number
conversion unit 111 will be explained in detail in the section
(2).
The motion compensation coding unit 107 extracts the image area
that is most suitable for the predictive image from among the
reconstructed image signals stored in the picture memory 105, using
the motion vectors estimated by the above-mentioned processing and
the reference indices. Pixel value conversion processing such as
interpolation processing by linear prediction is performed on the
pixel values of the obtained image area so as to obtain the final
predictive image. The linear prediction coefficients used for that
purpose are generated by the linear prediction coefficient
generation unit 110, and stored in the linear prediction
coefficient storage unit 109. This predictive image generation
method will be explained in detail in the section (3).
The coded stream generation unit 103 performs variable length
coding for the coded information such as the linear prediction
coefficients, the reference indices, the motion vectors and the
coded error signals outputted as a result of the above series of
processing so as to obtain a coded stream to be outputted from this
coding apparatus.
The flow of operations in the case of inter-picture prediction
coding has been described above, and a switch 114 and a switch 115
switch between inter-picture prediction coding and intra-picture
prediction coding. In the case of intra-picture prediction coding,
a predictive image is not generated by motion compensation, but a
difference image signal is generated by calculating a difference
between a current area and a predictive image of the current area
which is generated from a coded area in the same picture. The
prediction error coding unit 102 converts the difference image
signal into the coded error signal in the same manner as
inter-picture prediction coding, and the coded stream generation
unit 103 performs variable length coding for the signal to obtain a
coded stream to be outputted.
(2) Method for Assigning Reference Indices
Next, the method by which the reference index/picture number
conversion unit 111 as shown in FIG. 1 assigns reference indices
will be explained using FIG. 3 and FIG. 4.
FIG. 3 is a diagram for explaining the method for assigning two
reference indices to picture numbers. Supposing that there is a
sequence of pictures ordered in display order as shown in this
diagram, picture numbers are assigned to the pictures in coding
order. Commands for assigning reference indices to picture numbers
are described in a header of each slice that is a subdivision of a
picture, as the unit of coding, and thus the assignment thereof is
updated every time one slice is coded. The command indicates, in
series by the number of reference indices, the differential value
between a picture number which is assigned a reference index
currently and a picture number which is assigned a reference index
immediately before the current assignment.
Taking the first reference indices in FIG. 3 as an example, since
"-1" is given first as a command, a picture with its picture number
15 is assigned to the reference index number 0 by subtracting 1 to
the current picture number 16. Next, "-4" is given as a command, a
picture with its picture number 11 is assigned to the reference
index number 1 by subtracting 4 from the picture number 15 which
has been assigned just before it. Each of the following picture
numbers is assigned in the same manner. The same applies to the
second reference indices.
According to the conventional reference index assignment method as
shown in FIG. 34, all the reference indices are corresponded to
respective picture numbers. On the other hand, in the example of
FIG. 3, although exactly the same assignment method is used, a
plurality of reference indices are corresponded to the same picture
number by changing the values of the commands.
FIG. 4 shows the result of assignment of the reference indices.
This diagram shows that the first reference index and the second
reference index are assigned to each picture number separately, but
a plurality of reference indices are assigned to one picture number
in some cases. In the coding method of the present invention, it is
assumed that a plurality of reference indices are assigned to at
least one picture number, like this example.
If the reference indices are used only for determination of
reference pictures, the conventional method of one-to-one
assignment of reference indices to picture numbers is the most
efficient coding method. However, in the case where a weighting
coefficient set of linear prediction coefficients is selected for
generation of a predictive image using reference indices, the same
linear prediction coefficients have to be used for all the blocks
having the same reference pictures, so there is an extremely high
possibility that the optimum predictive image cannot be
generated.
So, if it is possible to assign a plurality of reference indices to
one picture number as in the case of the present invention, the
optimum weighting coefficient set of linear prediction coefficients
can be selected for each block from among a plurality of candidate
sets even if all the blocks have the same reference picture, and
thus the predictive image with its coding efficiency being higher
can be generated.
Note that, the above description shows the case where the picture
numbers are given assuming that all the reference pictures are
stored in a reference memory. However, a current picture is given a
picture number which is larger by one than the number of a picture
which has been coded immediately before the current picture, only
when the current picture which has been coded lastly is stored, so
the continuity of the picture numbers are maintained in the
reference memory even if some pictures are not stored, and thus the
above-mentioned method can be used without change.
(3) Method for Generating Predictive Image
Next, the predictive image generation method in the motion
compensation coding unit 107 as shown in FIG. 1 will be explained
using FIG. 5. Although the predictive image generation method by
linear prediction is exactly the same as the conventional method,
flexibility in selection of linear prediction coefficients is
increased because a plurality of reference index numbers can be
corresponded to the same picture.
The picture B16 is a current B-picture to be coded, and the blocks
BL01 and BL02 are current blocks to be coded which belong to the
B-picture. The picture P11 and the picture B15 are used as the
first reference picture and the second reference picture for BL01,
and the predictive image is generated with reference to the blocks
BL11 and BL21 belonging to the pictures P11 and B15 respectively.
In the same manner, the picture P11 and the picture B15 are used as
the first reference picture and the second reference picture for
BL02, the predictive image is generated with reference to the
blocks BL12 and BL22 belonging to those reference pictures
respectively.
Although both BL01 and BL02 refer to the same pictures as their
first reference picture and the second reference picture, it is
possible to assign different values to the first reference index
ref1 and the second reference index ref2 for BL01 and BL02 by using
the reference index assignment method as explained in the above
(2). Taking FIG. 4 as an example, 1 and 3 are assigned to the first
reference index corresponding to the picture number 11, whereas 1
and 6 are assigned to the second reference index corresponding to
the picture number 15.
As a result, four combinations of these reference indices, (ref1,
ref2)=(1, 1), (1, 6), (3, 1) and (3, 6) are supposed, and thus it
is possible to select the combination for deriving the optimum
weighting coefficient set on a per-block basis from among these
combinations. In FIG. 5, ref1=1 and ref2=1 are assigned for BL01,
and ref1=3 and ref2=6 are assigned for BL02, for example.
According to the conventional reference assignment method as shown
in FIG. 35, only one combination of (ref1, ref2)=(1, 1) can be
selected for both BL01 and BL02 in the case of FIG. 5, and thus
only one weighting coefficient set of linear prediction
coefficients can be selected, too. On the other hand, according to
the present invention, four options are available, and it can be
said that the possibility for selection of the optimum weighting
coefficient set is increased.
A coded stream of one picture is made up of a picture common
information area and a plurality of slice data areas. FIG. 6 shows
the structure of the slice data area in the coded stream. The slice
data area is further made up of a slice header area and a plurality
of block data areas. This diagram shows each of the block areas
corresponding to BL01 and BL02 in FIG. 5 as an example of the block
data area. "ref1" and "ref2" included in BL01 designate the first
reference index and the second reference index respectively
indicating two pictures referred to by the block BL01.
Also, in the slice header area, data (pset0, pset1, pset2, . . . )
for giving the weighting coefficient sets for performing the
above-mentioned linear prediction is described for ref1 and ref2
respectively. In this area, "pset"s of the number equivalent to the
number of the reference indices as explained in (2) can be set. To
be more specific, in the case where ten reference indices from 0 to
9 are used as each of the first reference index and the second
reference index, ten "pset" s from 0 to 9 can also be set for each
of ref1 and ref2.
FIG. 7 shows an example of tables of the weighting coefficient sets
included in the slice header area. Each data indicated by an
identifier pset has four values w1, w2, c and d, and these tables
are structured so that the data can be directly referred to by the
values of ref1 and ref2. Also, command sequences idx_cmd1 and
idx_cmd2 for assigning the reference indices to the picture numbers
are described in the slice header area.
Using ref1 and ref2 described in BL01 in FIG. 6, one set of
weighting coefficients is selected from each of the tables for ref1
and ref2 in FIG. 7. By performing linear prediction on the pixel
values of the reference images using these two sets of weighting
coefficients, a predictive image is generated.
As described above, using the coding method in which a plurality of
reference indices are assigned to one picture number, a plurality
of candidates for weighting coefficient sets of linear prediction
coefficients can be created, and thus the best one can be selected
from among them. For example, in the case where two first reference
indices and two second reference indices are assigned, four sets of
weighting coefficients are available as candidates for selection,
and in the case where three first reference indices and three
second reference indices are assigned, nine sets of weighting
coefficients are available as candidates for selection.
This linear prediction method has a dramatic effect particularly in
the case where the brightness of the entire picture or a part
thereof changes significantly like fade and flash. In many cases,
the degree of change in brightness differs from part to part of a
picture. Therefore, the structure of the present invention in which
the best one can be selected for each block from among a plurality
of weighting coefficient sets is very effective in image
coding.
Here, the flow of processing from determination of weighting
coefficient sets up to generation of a predictive image will be
explained in detail.
FIG. 8 is a functional block diagram showing the functional
structure for generating a predictive image in the linear
prediction coefficient generation unit 110, the linear prediction
coefficient storage unit 109 and the motion compensation coding
unit 107.
A predictive image is generated via the linear prediction
coefficient generation unit 110, the linear prediction coefficient
storage unit 109a, the linear prediction coefficient storage unit
109a, the average calculation unit 107a and the linear prediction
operation unit 107b.
The weighting coefficient sets generated by the linear prediction
coefficient generation unit 110 are stored in the linear prediction
coefficient storage unit 109a and the linear coefficient storage
unit 109b. The average calculation unit 107a obtains, from the
linear prediction coefficient storage unit 109a, one set of
weighting coefficients (w1.sub.--1, w2.sub.--1, c.sub.--1,
d.sub.--1) selected by the first reference index ref1 determined by
the motion estimation processing, and further obtains, from the
linear coefficient storage unit 109b, one set of weighting
coefficients (w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2)
selected by the second reference index ref2.
Then, the average calculation unit 107a calculates the average, for
respective parameters, of the weighting coefficient sets obtained
from the linear prediction coefficient storage units 109a and 109b
so as to consider it as the weighting coefficient set (w1, w2, c,
d) to be used for the actual linear prediction, and outputs it to
the linear prediction operation unit 107b. The linear prediction
operation unit 107b calculates the predictive image using the
equation 1 based on the obtained weighting coefficient set (w1, w2,
c, d) for output.
FIG. 9 is a functional block diagram showing another functional
structure for generating a predictive image. A predictive image is
generated via the linear prediction coefficient generation unit
110, the linear prediction coefficient storage unit 109a, the
linear prediction coefficient storage unit 109b, the linear
prediction operation unit 107c, the linear prediction operation
unit 107d and the average calculation unit 107e.
The weighting coefficient sets generated by the linear prediction
coefficient generation unit 110 are stored in the linear prediction
coefficient storage unit 109a and the linear prediction coefficient
storage unit 109b. The linear prediction operation unit 107c
obtains, from the linear prediction coefficient storage unit 109a,
one set of weighting coefficients (w1.sub.--1, w2.sub.--1,
c.sub.--1, d.sub.--1) selected by the first reference index refl
determined by the motion estimation processing, and calculates the
predictive image using the equation 1 based on the weighting
coefficient set for output to the average calculation unit
107e.
In the same manner, the linear prediction operation unit 107d
obtains, from the linear prediction coefficient storage unit 109b,
one set of weighting coefficient set (w1.sub.--2, w2.sub.--2,
c.sub.--2, d.sub.--2) selected by the second reference index
determined by the motion estimation processing, and calculates the
predictive image using the equation 1 based on the weighting
coefficient set for output to the average calculation unit
107e.
The average calculation unit 107e calculates the average of
respective pixel values of predictive images which are outputted
from the linear prediction operation unit 107c and the linear
prediction operation unit 107d respectively so as to generate the
final predictive image for output.
FIG. 10A is a functional block diagram showing another functional
structure for generating a predictive image. A predictive image is
generated via the linear prediction coefficient generation unit
110, the linear prediction coefficient storage unit 109c, the
linear prediction storage unit 109d, the average calculation unit
107f, and the linear prediction operation unit 107g.
The weighting coefficient sets generated by the linear prediction
coefficient generation unit 110 are stored in the linear prediction
coefficient storage unit 109c and the linear prediction coefficient
storage unit 109d. The average calculation unit 107f obtains, from
the linear prediction coefficient storage unit 109c, the parameters
of c.sub.--1 and d.sub.--1 in one set of weighting coefficients
(w1.sub.--1, w2.sub.--1, c.sub.--1, d.sub.--1) selected by the
first reference index refl determined by the motion estimation
processing, and similarly, obtains, from the linear prediction
coefficient storage unit 109d, the parameters of c.sub.--2 and
d.sub.--2 in one set of weighting coefficients (w1.sub.--2,
w2.sub.--2, c.sub.--2, d.sub.--2) selected by the second reference
index ref2. The average calculation unit 107f calculates the
average of c.sub.--1 and c.sub.--2 and the average of d.sub.--1 and
d.sub.--2 obtained from the linear prediction coefficient storage
unit 109c and the linear prediction coefficient storage unit 109d
so as to obtain c and d for output to the linear prediction
operation unit 107g.
Also, the linear prediction operation unit 107g obtains the
parameter of w1.sub.--1 in the above-mentioned weighting
coefficient set (w1.sub.--1, w2.sub.--1, c.sub.--1, d.sub.--1) from
the linear prediction coefficient storage unit 109c, obtains the
parameter of w2.sub.--2 in the above-mentioned weighting
coefficient set (w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2) from
the linear prediction coefficient storage unit 109d, and obtains c
and d which are the averages calculated by the average calculation
unit 107f, and then calculates the predictive image using the
equation 1 for output.
To be more specific, when determining the weighting coefficient set
(w1, w2, c, d) which is actually used for linear prediction from
among the weighting coefficient set (w1.sub.--2, w2.sub.--1,
c.sub.--1, d.sub.--1) obtained from the linear prediction
coefficient storage unit 109c and the weighting coefficient set
(w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2) obtained from the
linear prediction coefficient storage unit 109d, the linear
prediction operation unit 107g uses the following rule.
w1=w1.sub.--1 w2=w2.sub.--2 c=(average of c.sub.--1 and c.sub.--2)
d=(average of d.sub.--1 and d.sub.--2)
As described above, in generation of the predictive image as
explained in FIG. 10A, the linear prediction coefficient storage
unit 109c does not need w2.sub.--1 in the weighting coefficient
set. Therefore, w2 is not required for the weighting coefficient
set for ref1, and thus data amount of a coded stream can be
reduced.
Also, the linear prediction coefficient storage unit 109d does not
need w1.sub.--2 in the weighting coefficient set. Therefore, w1 is
not required for the weighting coefficient set for ref2, and thus
data amount of a coded stream can be reduced.
FIG. 10B is a functional block diagram showing another functional
structure for generating a predictive image. A predictive image is
generated via the linear prediction coefficient generation unit
110, the linear prediction coefficient storage unit 109e, the
linear prediction coefficient storage unit 109f and the linear
prediction operation unit 107h.
The weighting coefficient sets generated by the linear prediction
coefficient generation unit 110 are stored in the linear prediction
coefficient storage unit 109e and the linear prediction coefficient
storage unit 109f. The linear prediction operation unit 107h
obtains, from the linear prediction coefficient storage unit 109e,
the parameters of w1.sub.--1, c.sub.--1 and d.sub.--1 which are a
part of one set of weighting coefficients (w1.sub.--1, w2.sub.--1,
c.sub.--1, d.sub.--1) selected by the first reference index refl
determined by the motion estimation processing, and similarly,
obtains, from the linear prediction coefficient storage unit 109f,
the parameter of w2.sub.--2 which is a part of one set of weighting
coefficients (w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2)
selected based on the second reference index ref2. The linear
prediction operation unit 107h calculates a predictive image using
the equation 1 based on w1.sub.--1, c.sub.--1, d.sub.--1,
w2.sub.--2 obtained from the linear prediction coefficient storage
unit 109e and the linear prediction coefficient storage unit 109f
for output.
To be more specific, when determining the weighting coefficient set
(w1, w2, c, d) which is actually used for linear prediction from
among the weighting coefficient set (w1.sub.--1, w2.sub.--1,
c.sub.--1, d.sub.--1) obtained from the linear prediction
coefficient storage unit 109e and the weighting coefficient set
(w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2) obtained from the
linear prediction coefficient storage unit 109f, the linear
prediction operation unit 107h uses the following rule.
w1=w1.sub.--1 w2=w2.sub.--2 c=c.sub.--1 d=d.sub.--1
In generation of the predictive image as explained in FIG. 10B, the
linear prediction coefficient storage unit 109e does not need
w2.sub.--1 in the weighting coefficient set. Therefore, w2 is not
required for the weighting coefficient set for ref1, and thus data
amount of a coded stream can be reduced.
Also, the linear prediction coefficient storage unit 109f does not
need w1.sub.--2, c.sub.--2 and d.sub.--2 in the weighting
coefficient set. Therefore, w1, c and d are not required for the
weighting coefficient set for ref2, and thus data amount of a coded
stream can be reduced.
Furthermore, it is also possible to use one or more parameters out
of w1, w2, c and d as fixed values. FIG. 11 is a functional block
diagram in the case where only "d" as a fixed value is used for the
functional structure in FIG. 10A. A predictive image is generated
via the linear prediction coefficient generation unit 110, the
linear prediction coefficient storage unit 109i, the linear
prediction coefficient storage unit 109j, the average calculation
unit 107j and the linear prediction operation unit 107k.
The coefficients selected by the first reference index refl from
the linear prediction coefficient storage unit 109i are only
(w1.sub.--1, c.sub.--1), and the coefficients selected by the
second reference index ref 2 from the linear prediction coefficient
storage unit 109j are only (w2.sub.--2, c.sub.--2). The average
calculation unit 107j calculates the average of c.sub.--1 and
c.sub.--2 obtained from the linear prediction coefficient storage
unit 109i and the linear prediction coefficient storage unit 109j
so as to obtain "c" and outputs it to the linear prediction
operation unit 107k.
The linear prediction operation unit 107k obtains the parameter of
w1.sub.--1 from the linear prediction coefficient storage unit
109i, the parameter of w2.sub.--2 from the linear prediction
coefficient storage unit 109j, and the parameter of c from the
average calculation unit 107j, and then calculates the predictive
image based on the equation 1 using a predetermined fixed value as
a parameter of d, and outputs the predictive image. To be more
specific, the following values are entered as the coefficients (w1,
w2, c, d) of the equation 1. w1=w1.sub.--1 w2=w2.sub.--2 c=(average
of c.sub.--1 and c.sub.--2) d=(fixed value)
Assignment of the above values into the equation 1 provides the
following equation 1a.
P(i)=(w1.sub.--1.times.Q1(i)+w2.sub.--2.times.Q2(i))/pow(2,
d)+(c.sub.--1+c.sub.--2)/2 Equation 1a (where pow(2, d) indicates
the "d" th power of 2)
Furthermore, by modifying the equation 1a, the following equation
1b is obtained. It is possible for the linear prediction operation
unit 107k to handle the linear prediction operation method in
exactly the same manner in either format of the equation 1b or the
equation 1. P(i)=(w1.sub.--1.times.Q1(i)/pow(2,
d-1)+c.sub.--1+w2.sub.--2.times.Q2(i)/pow(2, d-1)+c.sub.--2)/2
Equation 1b (where pow(2, d-1) indicates the "d-1"th power of
2)
Although pow(2, d-1) is used in the equation 1b, the system may be
structured using pow(2, d') by entering d' (assuming d'=d-1) into
the linear prediction operation unit 107k because d is a fixed
value.
In addition, in generation of the predictive image as explained in
FIG. 11, the linear prediction coefficient storage unit 109i needs
only w1.sub.--1 and c.sub.--1 among the weighting coefficient sets
for it, and the linear prediction coefficient storage unit 109j
needs only w2.sub.--2 and c.sub.--2 among the weighting coefficient
sets for it. Therefore, there is no need to code the parameters
other than the above required parameters, and thus the data amount
of the coded stream can be reduced.
Note that it is possible to use one predetermined fixed value as a
value of d in any cases, but the fixed value can be switched on a
per-slice basis by describing the fixed value in the slice header.
Similarly, the fixed value can be switched on a per-picture basis
or a per-sequence basis by describing it in the picture common
information area or the sequence common information area.
FIG. 12 shows an example of a structure of a slice data area in the
case where the above-mentioned linear prediction method is used.
This is different from FIG. 6 in that only "d" is described in the
slice header area and only w1.sub.--1 and c.sub.--1 are described
as pset for refl. FIG. 13 shows tables showing an example of the
above weighting coefficient sets included in the slice header area.
Each data indicated by the identifier "pset" has two values of
w1.sub.--1 and c.sub.--1 or w2.sub.--2 and c.sub.--2, and
structured so as to be directly referred to by the values of ref1
and ref2.
Note that the linear prediction coefficient generation unit 110
generates the weighting coefficient sets by examining the
characteristics of a picture, and the motion compensation coding
unit 107 creates a predictive image using any of the methods as
explained in FIG. 8, FIG. 9, FIG. 10 and FIG. 11 and determines the
combination of two reference indices ref1 and ref2 so as to
minimize the prediction error. In the case where any of the methods
of FIG. 10A, FIG. 10B and FIG. 11 which do not require all the
parameters is used, it is possible to omit the processing of
creating unnecessary parameters in the stage where the linear
prediction coefficient generation unit 110 in the coding apparatus
creates the weighting coefficient sets.
In the methods of FIG. 10A, FIG. 10B and FIG. 11, it is possible
for the linear prediction coefficient generation unit 110 to search
for and create the optimum weighting coefficient sets for ref1 and
ref2, w1.sub.--1 and w2.sub.--2, for example, separately, when
creating such weighting coefficient sets. In other words, using
these methods, it is possible to reduce the amount of processing
executed by the coding apparatus for creating weighting coefficient
sets.
Note that the above-mentioned coding methods are concerned with a
B-picture having two reference pictures, but it is also possible to
execute the same processing in the single picture reference coding
mode for a P-picture or a B-picture having only one reference
picture. In this case, using only one of the first reference index
and the second reference index, pset and idx_cmd for either ref1 or
ref2 are only described in the slice header area included in the
coded stream of FIG. 6, according to the reference index described
in the block data area.
In addition, as a linear prediction method, the following equation
3 is used instead of the equation 1 as explained in the
conventional method. In this case, Q1(i) is a pixel value of a
block which is referred to, P(i) is a pixel value of a predictive
image of a current block to be coded, and w1, w2, c and d are
linear prediction coefficients given by the selected weighting
coefficient set. P(i)=(w1.times.Q1(i)+w2.times.Q1(i))/pow(2, d)+c
Equation 3 (where pow(2, d) indicates the "d" th power of 2)
Note that it is possible to use the equation 4 as a linear
prediction equation, instead of the equation 3. In this case, Q1(i)
is a pixel value of a block which is referred to, P(i) is a pixel
value of a predictive image of a current block to be coded, and w1,
c and d are linear prediction coefficients given by the selected
weighting coefficient set. P(i)=(w1.times.Q1(i))/pow(2, d)+c
Equation 4 (where pow(2, d) indicates the "d" th power of 2)
Use of the equation 1 and the equation 3 requires four parameters
w1, w2, c and d, whereas use of the equation 4 requires only three
parameters w1, c and d for linear prediction. In other words, in
the case where either one of the first reference index and the
second reference index is used for a picture as a whole, like a
P-picture, it is possible to reduce the number of data items of
each weighting coefficient set to be described in the slice header
area to three.
When the equation 3 is used, it is possible to realize linear
prediction which is available for both B-pictures and P-pictures
adaptively without change in structure. When the equation 4 is
used, the data amount to be described in the header area of a
P-picture can be reduced, and thus it is possible to achieve
reduction of the processing amount because of simplified
calculation. However, since the reference index assignment method
suggested by the present invention can directly be applied to any
of the above methods, a predictive image with its high coding
efficiency can be created, which is extremely effective in image
coding.
By the way, the pictures which are referred to in motion
compensation are determined by designating the reference indices
assigned to respective pictures. In that case, the maximum number
of pictures which are available for reference has been described in
the picture common information area in the coded stream.
FIG. 38 is a schematic diagram of a coded stream in which the
maximum number of pictures which are available for reference is
described. As this diagram shows, the maximum number of pictures
for ref1 Max_pic1 and the maximum number of pictures for ref2
Max_pic2 are described in the picture common information in the
coded stream.
Information required for coding is not the maximum number of real
pictures themselves, but the maximum reference index value
available for designating pictures.
Since one reference index is assigned to one picture in the
conventional method, the above-mentioned description of the maximum
number of pictures causes no contradiction. But the difference in
number between reference indices and pictures has a significant
influence on the case where a plurality of reference indices are
assigned to one picture number, like the present invention.
As described above, command sequences idx_cmd1 and idx_cmd2 are
described in a coded stream in order to assign reference indices to
picture numbers. The picture numbers and the reference indices are
corresponded to each other based on each command in these command
sequences idx_cmd1 and idx_cmd2. For that purpose, knowing the
maximum reference index value shows that all the reference indices
and picture numbers have been corresponded to each other, namely,
the end of the commands in the command sequences idx_cmd1 and
idx_cmd2.
Therefore, in the present embodiment, the maximum number of
available reference indices, instead of the maximum number of
pictures in the background art, is described in the picture common
information area being the header of the picture. Or, both of the
maximum number of pictures and the maximum number of reference
indices are described.
FIG. 23 shows a picture common information area in a coded stream
of a picture in which the maximum numbers of reference indices are
described. In the picture common information area, the maximum
number of reference indices available for ref1 Max_idx1 and the
maximum number of reference indices available for ref2 Max_idx2 are
described.
In FIG. 23, the maximum number of reference indices is described in
the picture common information, but it may be structured so that
the maximum number of reference indices is described in the slice
data area as well as in the picture common information. For
example, the maximum number of reference indices required for each
slice can be clearly described, in the case where the maximum
number of required reference indices for each slice is
significantly different from the maximum number thereof described
in the picture common information area, from slice to slice, for
example, the maximum number of reference indices in a picture is 8,
the maximum number of reference indices required for the slice 1 in
the picture is 8, and the maximum number of reference indices
required for the slice 2 is 4.
In other words, it may be structured so that the maximum number of
reference indices described in the picture common information is
set as a default value common to all the slices in the picture and
the maximum number of reference indices required for a slice, which
is different from the default value, is described in the slice
header.
Although FIG. 23 and FIG. 38 show the examples where a coded stream
is made up of a picture common information area and slice data
areas, the picture common information area and the slice data areas
can be handled as separate coded streams in exactly the same manner
as one coded stream.
Second Embodiment
The moving picture coding method in the second embodiment of the
present invention will be explained. Since the structure of the
coding apparatus, the flow of coding processing and the reference
index assignment method are exactly the same as those in the first
embodiment, the explanation thereof is not repeated here.
In the first embodiment, linear prediction is performed on each
pixel for generating a predictive image in motion compensation
using the equation 1, the equation 3 or the equation 4. However,
since all of these equations include multiplications, which cause
significant increase of processing amount in considering that these
multiplications are performed on all the pixels.
So, it is possible to use the equation 5 instead of the equation 1,
the equation 6 instead of the equation 3, and the equation 7
instead of the equation 4. These equations allow calculations only
using bit shift operations without using multiplications, and thus
allows reduction of processing amount. In the following equations,
Q1(i) and Q2(i) are pixel values of referred blocks, P(i) is a
pixel value of a predictive image of a current block to be coded,
and m, n and c are linear prediction coefficients given by a
selected weighting coefficient set. P(i)=.+-.pow(2,
m).times.Q1(i).+-.pow(2, n).times.Q2(i)+c Equation 5
P(i)=.+-.pow(2, m).times.Q1(i).+-.pow(2, n).times.Q1(i)+c Equation
6 P(i)=.+-.pow(2, m).times.Q1(i)+c Equation 7 (where pow(2, m)
indicates "m"th power of 2, and pow(2, n) indicates "n"th power of
2)
As is the case. with the first embodiment, the equation 5 is used
for generating a predictive image with reference to two pictures at
a time, and the equation 6 or the equation 7 is used for generating
a predictive image with reference to only one picture. Since these
equations require identifiers indicating plus and minus signs,
weighting coefficient sets required for prediction operations are
(sign1, m, sign2, n, c) for the equations 5 and 6, and (sign1, m,
c) for the equation 7. "sing1" and "sign2" are parameters
identifying the first and second plus and minus signs,
respectively. Although the number of parameters is larger than that
in the first embodiment, there is little increase in processing
amount because both sign1 and sign2 can be represented by 1
bit.
Here, the flow of processing from determination of weighting
coefficient sets until generation of a predictive image with
reference to two pictures at a time using the equation 5 will be
explained in detail.
First, the case where the functional structure for generation of a
predictive image is that as shown in FIG. 8 will be explained. The
average calculation unit 107a obtains the weighting coefficient set
(sign1.sub.--1, m.sub.--1, sign2.sub.--1, n.sub.--1, c.sub.--1)
from the linear prediction coefficient storage unit 109a. Also, the
average calculation unit 107a obtains the weighting coefficient set
(sign1.sub.--2, m.sub.--2, sign2.sub.--2, n.sub.--2, c.sub.--2)
from the linear prediction coefficient storage unit 109b.
The average calculation unit 107a calculates, for respective
parameters, the average of the weighting coefficient sets obtained
from the linear prediction coefficient storage unit 109a and the
linear prediction coefficient storage unit 109b so as to consider
the average as the weighting coefficient set (sign1, m, sign2, n,
c). The linear prediction operation unit 107b calculates the
predictive image using the equation 5 based on the weighting
coefficient set (sign1, m, sign2, n, c) outputted from the average
calculation unit 107a.
Note that FIG. 8 shows the weighting coefficient set (w1.sub.--1,
w2.sub.--1, c.sub.--1, d.sub.--1) and the like obtained from the
linear prediction coefficient storage unit 109a and the like, which
are calculated in the case where the equation 1 is used as
explained in the first embodiment, and does not show the parameters
used in the case where the predictive image is obtained using the
equation 5, but the parameters used in the former case can be
replaced by the parameters in the latter case as they are. The same
goes for the cases of FIG. 9 and FIG. 10 to be described later.
Next, the case where the functional structure for generation of a
predictive image is that as shown in FIG. 9 will be explained. The
linear prediction operation unit 107c calculates a predictive image
1 based on the weighting coefficient set (sign1.sub.--1, m.sub.--1,
sign2.sub.--1, n.sub.--1, c.sub.--1) obtained from the linear
prediction coefficient storage unit 109a. The linear prediction
operation unit 107d calculates a predictive image 2 based on the
weighting coefficient set (sign1.sub.--2, m.sub.--2, sign2.sub.--2,
n.sub.--2, c.sub.--2) obtained from the linear prediction
coefficient storage unit 109b. And the average calculation unit
107e calculates, for respective pixels, the average of the
predictive images calculated by the linear prediction operation
units 107c and 107d so as to obtain a predictive image.
In this case, the linear prediction operation unit 107c first
calculates the predictive image using the equation 5 based on the
weighting coefficient set (sign1.sub.--1, m.sub.--1, sign2.sub.--1,
n.sub.--1, c.sub.--1), so it is possible to calculate the
predictive image using bit shift operations without using
multiplications. The same goes for the linear prediction operation
unit 107d. On the other hand, in the case of FIG. 8, since the
average of the weighting coefficient set (sign1.sub.--1, m.sub.--1,
sign2.sub.--1, n.sub.--1, c.sub.--1) and the weighting coefficient
set (sign1.sub.--2, m.sub.--2, sign2.sub.--2, n.sub.--2, c.sub.--2)
is calculated first, the average of m.sub.--1and m.sub.--2or the
average of n.sub.--1 and n.sub.--2, namely, the exponents of 2,
could not be integers, and thus there is a possibility that the
processing amount increases. Also, if the exponents of 2 are
rounded off to integers, there is another possibility that the
error increases.
Next, the case where a predictive image is generated in the
functional structure as shown in FIG. 10A will be explained. The
linear prediction operation unit 107g calculates a predictive image
using the equation 5, based on the parameters sign1.sub.--1 and
m.sub.--1which are obtained from the linear prediction coefficient
storage unit 109c and used for bit shift operations; the parameters
sign2.sub.--2 and n.sub.--2 which are obtained from the linear
prediction coefficient storage unit 109d and used for bit shift
operations; and the average c calculated by the average calculation
unit 107f, of the parameters c.sub.--1 and c.sub.--2 which are
obtained from the linear prediction coefficient storage units 109c
and 109d.
In this case, since the coefficients used for bit shift operations
are the values which are obtained directly from the linear
prediction coefficient storage unit 109c or the linear prediction
coefficient storage unit 109d, the exponents of 2 in the equation 5
are integers. Therefore, the calculations can be performed using
bit shift operations, and thus the processing amount can be
reduced.
The case where a predictive image is generated in the functional
structure as shown in FIG. 10B will be explained. The linear
prediction operation unit 107h calculates a predictive image using
the equation 5 based on the parameters sign1.sub.--1, m.sub.--1 and
c.sub.--1 which are obtained from the linear prediction coefficient
storage unit 109e and the parameters sign2.sub.--2 and n.sub.--2
which are obtained from the linear prediction coefficient storage
unit 109f.
In this case, since the coefficients used for bit shift operations
are values which are obtained directly from the linear prediction
coefficient storage unit 109e or the linear prediction coefficient
storage unit 109f, the exponents of 2 in the equation 5 are
integers. Therefore, the predictive image can be calculated using
bit shift operations, and thus the processing amount can be
reduced.
In the cases of FIGS. 10A and 10B, there are parameters which do
not need to be added to the coded stream for transmission, as is
the case with the cases of FIGS. 10A and 10B in the first
embodiment, and the data amount of the coded stream can be
reduced.
Using the linear prediction equations as explained in the second
embodiment, the calculations can be performed using bit shift
operations without using multiplications, so the processing amount
can be significantly reduced from that in the first embodiment.
In the present embodiment, linear prediction is performed using the
equations 5, 6 and 7 instead of the equations 1, 3 and 4, and using
the parameter set to be coded (sign1, m, sign2, n, c) instead of
(w1, w2, c, d), so the calculations can be realized only using bit
shift operations and thus reduction of processing amount is
achieved. However, it is also possible, as another approach, to use
the equations 1, 3 and 4 and (w1, w2, c, d) as they are, by
limiting the selectable values of w1 and w2 to only the values
available for bit shift operations, so the calculations can be
realized only using bit shift operations and thus reduction of
processing amount is achieved.
When determining the values of w1 and w2, the linear prediction
coefficient generation unit 110 in FIG. 1 selects, as one of the
choices, only the values available for bit shift operations and
describes the selected values directly into the coded streams in
FIG. 6 and FIG. 12, as the values of w1 and w2 therein. As a
result, it is possible to reduce the processing amount for linear
prediction even in exactly the same structure as that of the first
embodiment. It is also possible to determine the coefficients
easily because the choices of the coefficients are limited.
In addition, as a method for such limitation, it is possible to
limit the values of w1 and w2 so that 1 is always selected for such
values and generate the optimum values of only c1 and c2, which are
DC components, in the linear prediction coefficient generation unit
110. Taking the structure of FIG. 11 as an example, (1, c.sub.--1)
for ref1 and (1, c.sub.--2) for ref2 are coded as parameter sets.
In this case, the pixel value P(i) of the predictive image is
calculated by the following equation in which w1.sub.--1 and
w2.sub.--2 in the equation 1a are substituted for 1.
P(i)=(Q1(i)+Q2(i))/pow(2, d)+(c.sub.--1+c.sub.--2)/2 (where pow(2,
d) indicates the "d"th power of 2)
Accordingly, it is possible to significantly reduce the processing
amount for linear prediction even in exactly the same structure as
that of the first embodiment. It is also possible to significantly
simplify the method for determining coefficients because necessary
coefficients are only c.sub.--1 and c.sub.--2.
FIG. 24 shows an example where a flag sft_flg, indicating whether
or not it is possible to perform linear prediction using only bit
shift operations, and a flag dc_flg, indicating whether or not it
is possible to perform linear prediction using only c that is a DC
component, are described in picture common information in a coded
stream of a picture. A decoding apparatus can decode the picture
without reference to these flags. However, referring to these
flags, it is possible to perform decoding in the structure suitable
for linear prediction using only bit shift operations or decoding
in the structure suitable for linear prediction using only a DC
component, so these flags could be very important information
depending on the structure of the decoding apparatus.
Although FIG. 24 shows the example where a coded stream is made up
of a picture common information area and slice data areas, the
picture common information area and the slice data areas can be
handled as separate coded streams in exactly the same manner as one
coded stream. Also, in the example of FIG. 24, sft_flg and dc_flg
are described in the picture common information area, but they can
be handled in exactly the same manner even if they are described in
the sequence common information area or another independent common
information area. In addition, it is possible not only to use both
of these two flags sft_flg and dc_flg at the same time, but also to
use either one of them, and they can be handled in the same manner
in the latter case.
Third Embodiment
The moving picture coding method in the third embodiment of the
present invention will be explained. Since the structure of the
coding apparatus, the flow of coding processing and the reference
index assignment method are exactly same as those in the first
embodiment, the explanation thereof is not repeated here.
As explained in the background art, there is a method for
generating a predictive image using a predetermined fixed equation
such as the equation 2a and the equation 2b, unlike the first and
second embodiments in which a predictive image is generated using a
prediction equation obtained from weighting coefficient sets of
linear prediction coefficients. This conventional method has an
advantage that a data amount for coding can be reduced because
there is no need to code and transmit the weighting coefficient
sets used for generating the predictive image. Also, the processing
amount for linear prediction can be significantly reduced because
the equations for linear prediction are simple. However, the method
using the fixed equations has a problem that prediction accuracy is
lowered because there are only two selectable linear prediction
equations 2a and 2b.
So, in the present embodiment, the equations 8a and 8b are used
instead of the equations 2a and 2b. These equations 8a and 8b are
obtained by adding C1 and C2 to the equations 2a and 2b. Since only
the number of additions increases for the operation, there is
little increase in processing amount, compared with the original
equations 2a and 2b. In the following equations, Q1(i) and Q2(i)
are pixel values ofreferred blocks, P(i) is a pixel value of a
predictive image of a current block to be coded, and C1 and C2 are
linear prediction coefficients given by a selected weighting
coefficient set. P(i)=2.times.(Q1(i)+C1)-(Q2(i)+C2) Equation 8a
P(i)=(Q1(i)+C1+Q2(i)+C2)/2 Equation 8b
The equations 8a and 8b are prediction equations for generating a
predictive image with reference to two pictures at a time, but when
generating a predictive image with reference to only one picture,
the equation 9 is used instead of the equation 3 or 4 as explained
in the above embodiments. P(i)=Q1(i)+C1 Equation 9
The weighting coefficient sets for using this method are only (C1)
for ref1 and (C2) for ref2. Therefore, an example of a coded stream
of a picture obtained using this method is as shown in FIG. 14. In
the slice header area, the weighting coefficient sets for linear
prediction (pset0, pset1, pset2, . . . ) are described for ref1 and
ref2 separately, and each of the weighting coefficient sets
includes only C. Similarly, FIG. 15 shows an example of weighting
coefficient sets included in the slice header area. Differently
from FIG. 7, each of the weighting coefficient sets in FIG. 15
includes only C.
FIG. 16 is a block diagram showing the functional structure for
generating a predictive image via the linear prediction coefficient
generation unit 110, the linear prediction coefficient storage unit
109 and the motion compensation coding unit 107 in FIG. 1.
A predictive image is generated via the linear prediction
coefficient generation unit 110, the linear prediction coefficient
storage unit 109g, the linear prediction coefficient storage unit
109h and the linear prediction operation unit 107i.
The weighting coefficient sets generated by the linear prediction
coefficient generation unit 110 are stored in the linear prediction
coefficient storage unit 109g and the linear prediction coefficient
storage unit 109h. Using the first reference index ref1 and the
second reference index ref2 determined by the motion estimation
processing, the weighting coefficient sets (C1) and (C2) having one
element respectively are obtained from the linear prediction
coefficient storage units 109g and 109h. These values are inputted
to the linear prediction operation unit 107i, where linear
prediction is performed on them using the equations 8a and 8b, and
then the predictive image is generated.
Similarly, when linear prediction is performed with reference to
only one picture, either one of the weighting coefficient sets (C1)
and (C2) is obtained using only one of ref1 and ref2 in FIG. 16,
linear prediction is performed using the equation 9, and then the
predictive image is generated.
Note that the linear prediction coefficient generation unit 110
generates the weighting coefficient sets (C1) and (C2) by examining
the characteristics of a picture, creates a predictive image using
the method as explained in FIG. 16, and then determines a
combination of the two reference indices ref1 and ref2 so as to
minimize the prediction error.
Since the present embodiment requires only one parameter to be used
for each of ref1 and ref2, the coding apparatus can determine the
values of parameters easily and further the data amount to be
described in the coded stream can be reduced. Also, since the
linear prediction equations do not require complicated operations
such as multiplications, the operation amount can also be
minimized. In addition, the use of the coefficients C1 and C2
allows dramatic improvement of the low prediction accuracy, which
is considered as a disadvantage of the conventional method of using
a fixed equation.
Note that it is possible to use the linear prediction method as
explained in the present embodiment, regardless of whether a
plurality of reference indices can refer to the same picture or
not.
Fourth Embodiment
The moving picture coding method in the fourth embodiment of the
present invention will be explained. Since the structure of the
coding apparatus, the flow of coding processing and the reference
index assignment method are exactly same as those in the first
embodiment, the explanation thereof is not repeated here.
Display order information indicating display time or the
alternative thereto as well as a picture number are assigned to
each picture. FIG. 39 is a diagram showing an example of picture
numbers and the corresponding display order information. Certain
values are assigned to the display order information according to
display order. In this example, the value which increases one by
one for each picture is used. A method for generating values of
coefficients used in an equation for linear prediction using this
display order information will be explained in the fourth
embodiment.
In the first embodiment, linear prediction is performed for each
pixel using the equation 1, the equation 3 or the equation 4 when
generating a predictive image in motion compensation. However,
since the linear prediction requires data of coefficients, such
coefficient data is described in slice header areas in a coded
stream as weighting coefficient sets to be used for creation of the
predictive image. Although this method achieves high coding
efficiency, it requires additional processing for creating data of
the weighting coefficient sets and causes increase in bit amount
because the weighting coefficient sets are described in the coded
stream.
So, it is also possible to perform linear prediction using the
equation 10, equation 11a and the equation 12a instead of the
equation 1. Using these equations, the weighting coefficients can
be determined based on only the display order information of each
reference picture, so there is no need to code the weighting
coefficient sets separately.
In the following equations, Q1(i) and Q2(i) are pixel values of
referred blocks, P(i) is a pixel value of a predictive image of a
current block to be coded, V0 and V1 are weighting coefficients, T0
is the display order information of the current picture to be
coded, T1 is the display order information of the picture
designated by the first reference index, and T2 is the display
order information of the picture designated by the second reference
index. P(i)=V1.times.Q1(i)+V2.times.Q2(i) Equation 10
V1=(T2-T0)/(T2-T1) Equation 11a V2=(T0-T1)/(T2-T1) Equation 12a
When it is assumed, as an example, that the current picture to be
coded is No. 16, the picture designated by the first reference
index is No. 11, and the picture designated by the second reference
index is No. 10, the display order information of respective
pictures are 15, 13 and 10, and thus the following linear
prediction equations are determined. V1=(10-15)/(10-13)=5/3
V2=(15-13)/(10-13)=-2/3 P(i)=5/3.times.Q1(i)-2/3.times.Q2(i)
Compared with the method for performing linear prediction using the
weighting coefficient sets in the equation 1, the above equations
have lower flexibility of coefficient values, and thus it can be
said that it is impossible to create the optimum predictive image.
However, compared with the method of switching the two fixed
equations 2a and 2b depending on the positional relationship
between two reference pictures, the above equations are more
efficient linear prediction equations.
When both the first reference index and the second reference index
refer to the same picture, the equation 11a and the equation 12a do
not hold because T1 becomes equal to T2. So, when the two reference
pictures have the same display order information, linear prediction
shall be performed using 1/2 as the values of V1 and V2. In that
case, the linear prediction equations are as follows. V1= 1/2 V2=
1/2 P(i)=1/2.times.Q1(i)+1/2Q2(i)
Also, the equations 11a and 12a do not hold because T1 becomes
equal to T2 when the first reference index and the second reference
index refer to different pictures but these pictures have the same
display order information. When the two reference pictures have the
same display order information as mentioned above, linear
prediction shall be performed using 1/2 as the values of V1 and
V2.
As described above, when two reference pictures have the same
display order information, it is possible to use a predetermined
value as a coefficient. Such predetermined coefficient may be one
having the same weight like 1/2 as shown in the above example.
By the way, use of the equation 10 in the above embodiments
requires multiplications and divisions for linear prediction. Since
the linear prediction operation using the equation 10 is the
operation for all the pixels in a current block to be coded,
addition of multiplications causes significant increase in the
processing amount.
So, approximation of V1 and V2 to the powers of 2 like the case of
the second embodiment makes it possible to perform linear
prediction operation using only shift operations, and thus to
achieve reduction of the processing amount. As the linear
prediction equations for that case, the equations 11b and 12b are
used instead of the equations 11a and 12a. In the following
equations, v1 and v2 shall be integers. V1=.+-.pow(2,
v1)=apx((T2-T0)/(T2-T1)) Equation 11b V2=.+-.pow(2,
v2)=apx((T0-T1)/(T2-T1)) Equation 12b (where pow(2, v1) indicates
the "v1"th power of 2 and pow(2, v2) indicates the "v2"th power of
2) (where=apx( ) indicates that the value in ( ) shall be
approximated to the left-hand value)
Note that it is also possible to use the equations 11c and 12c
instead of the equations 11a and 12a, where v1 is an integer.
V1=.+-.pow(2, v1)=apx((T2-T0)/(T2-T1)) Equation 11c V2=1-V1
Equation 12c (where pow(2, v1) indicates the "v1"th power of 2)
(where=apx( ) indicates that the value in ( ) shall be approximated
to the left-hand value)
Note that it is also possible to use the equations 11d and 12d
instead of the equations 11a and 12a, where v1 is an integer.
V1=1-V2 Equation 11d V2=.+-.pow(2, v2)=apx((T0-T1)/(T2-T1))
Equation 12d (where pow(2, v2) indicates the "v2"th power of 2)
(where=apx( ) indicates that the value in ( ) shall be approximated
to the left-hand value)
Note that the value of V1 and V2 approximated to the power of 2
shall be, taking the equation 1b as an example, the value of
.+-.pow(2, v1) obtained when the values of .+-.pow(2, v1) and
(T2-T0)/(T2-T1) are mostly approximated to each other as the value
of v1 changes one by one.
For example, in FIG. 39, when a current picture to be coded is No.
16, the picture designated by the first reference index is No. 11,
and the picture designated by the second reference index is No. 10,
the display order information of the respective pictures are 15, 13
and 10, so (T2-T0)/(T2-T1) and .+-.pow(2, v1) are as follows.
(T2-T0)/(T2-T1)=(10-15)/(10-13)=5/3 +pow(2, 0)=1 +pow(2, 1)=2
Since 5/3 is close to 2 rather than 1, V1=2 is obtained as a result
of approximation.
As another approximation method, it is also possible to switch
between round-up approximation and round-down approximation
depending on the relationship between two values of display order
information T1 and T2.
In that case, round-up approximation is performed on both V1 and V2
when T1 is later than T2, and round-down approximation is performed
on both V1 and V2 when T1 is earlier than T2. It is also possible,
in a reverse manner, to perform round-down approximation on both V1
and V2 when T1 is later than T2, and round-up approximation on both
V1 and V2 when T1 is earlier than T2.
As another approximation method using display order information,
round-up approximation is performed in an equation for V1 and
round-down approximation is performed in an equation for V2 when T1
is later than T2. As a result, the difference between the values of
the two coefficients becomes large, it is likely that values
suitable for extrapolation are obtained. On the contrary, when T1
is earlier than T2, the value in the equation for V1 and the value
in the equation for V2 are compared, and then round-up
approximation is performed on the smaller value and round-down
approximation is performed on the larger value. As a result, the
difference between the values of the two coefficients becomes
small, so it is likely that values suitable for interpolation are
obtained.
For example, in FIG. 39, when a current picture to be coded is No.
16, the picture designated by the first reference index is No. 11,
and the picture designated by the second reference index is No. 10,
the display order information of the respective pictures are 15, 13
and 10. Since T1 is later than T2, round-up approximation is
performed on the equation for V1 and round-down approximation is
performed on the equation for V2. As a result, the equations 11b
and 12b are calculated as follows.
(T2-T0)/(T2-T1)=(10-15)/(10-13)=5/3 +pow(2, 0)=1 +pow(2, 1)=2 (1)
Equation 11b
As a result of round-up approximation, V1=2 is obtained.
(T0-T1)/(T2-T1)=(15-13)/(10-13)=-2/3 -pow(2, 0)=-1 -pow(2, -1)=-1/2
(2) Equation 12b
As a result of round-down approximation, V2=-1 is obtained. Note
that although the equation 10 is only one equation for liner
prediction in the above embodiments, it is also possible to combine
this method with the linear prediction method by use of the two
fixed equations 2a and 2b as explained in the background art. In
that case, the equation 10 is used instead of the equation 2a, and
the equation 2b is used as it is. In other words, the equation 10
is used when the picture designated by the first reference index
appears behind the picture designated by the second reference index
in display order, whereas the equation 2b is used in other
cases.
It is also possible, on the contrary, to use the equation 10
instead of the equation 2b and use the equation 2a as it is. In
other words, the equation 2a is used when the picture designated by
the first reference index appears behind the picture designated by
the second reference index, and the equation 10 is used in other
cases. However, when two reference pictures have the same display
order information, linear prediction is performed using 1/2 as the
values of V1 and V2.
It is also possible to describe only the coefficient C in the slice
header areas to be used for linear prediction, in the same manner
as the concept of the third embodiment. In that case, the equation
13 is used instead of the equation 10. V1 and V2 are obtained in
the same manner as the above embodiments.
P(i)=V1.times.(Q1(i)+C1)+V2.times.(Q2(i)+C2) Equation 13
The processing for generating coefficients C is needed, and further
the coefficients C needs to be coded into the slice header area,
but use of C1 and C2 allows more accurate linear prediction even if
the accuracy of V1 and V2 is low. This is effective particularly in
the case where V1 and V2 are approximated to the powers of 2 for
performing linear prediction.
Note that using the equation 13, the linear prediction can be
performed in the same manner in both cases where one reference
index is assigned to one picture and a plurality of reference
indices are assigned to one picture.
In the calculation of the values in each of the equations 11a, 12a,
11b, 12b, 11c, 12c, 11d and 12d, the combinations of available
values are limited to some extent in every slice. So, only one
operation is enough for coding a slice, unlike the equation 10 or
the equation 13 in which the operation needs to be performed for
all the pixels in a current block to be coded, and thus there seems
to be little influence on the entire processing amount.
Note that the display order information in the present embodiment
is not limited to display order, but may be the actual display
time, or the order of respective pictures starting from a
predetermined picture, with its value increasing as the lapse of
display time.
Fifth Embodiment
The moving picture coding method in the fifth embodiment of the
present invention will be explained. Since the structure of the
coding apparatus, the flow of coding processing and the reference
index assignment method are exactly same as those in the first
embodiment, the explanation thereof is not repeated here.
In the conventional method, it is possible to switch between
generation of a predictive image by use of fixed equations and
generation of a predictive image by use of weighting coefficient
sets of linear prediction coefficients, using flags described in a
picture common information area in a coded stream, if
necessary.
In the present embodiment, another method for switching the various
linear prediction methods as explained in the above first to fourth
embodiments using flags will be explained.
FIG. 17A shows the structure used for the case where five flags
(p_flag, c_flag, d_flag, t_flag, s_flag) for controlling the above
switching are described in the slice header area in the coded
stream.
As shown in FIG. 17B, p_flag is a flag indicating whether weighting
coefficients have been coded or not. c_flag is a flag indicating
whether only the data of the parameter C (C1 and C2), out of the
parameters for ref1 and ref2, has been coded or not. t_flag is a
flag indicating whether weighting coefficients for linear
prediction are to be generated or not using the display order
information of the reference pictures. And s_flag is a flag
indicating whether the weighting coefficients for linear prediction
are to be approximated to the powers of 2 or not for the
calculation by use of shift operations.
Furthermore, d_flag is a flag indicating whether or not to switch
two predetermined fixed equations like the equations 2a and 2b
depending on the temporal positional relationship between the
picture designated by ref1 and the picture designated by ref2, when
linear prediction is performed using such two fixed equations. To
be more specific, when this flag indicates the switching of the
equations, the equation 2a is used in the case where the picture
designated by ref1 is later than the picture designated by ref2 in
display order, and the equation 2b is used in other cases for
performing linear prediction, as is the case with the conventional
method. On the other hand, when this flag indicates no switching of
the equations, the equation 2b is always used for performing linear
prediction, regardless of the positional relationship between the
picture designated by ref1 and the picture designated by ref2.
Note that even if the equation 2a is used instead of the equation
2b as an equation to be used without switching, the equation 2a can
be handled in the same manner as the equation 2b.
In the coding apparatus as shown in FIG. 1, the motion compensation
coding unit 107 determines whether or not to code the data
concerning the weighting coefficient sets on a per-slice basis,
outputs the information of the flag p_flag to the coded stream
generation unit 103 based on the determination, and describes the
information in the coded stream as shown in FIG. 17A. As a result,
it is possible to use the weighting coefficient sets in a higher
performance apparatus for performing linear prediction, and not to
use the weighting coefficient sets in a lower performance apparatus
for performing linear prediction.
Similarly, in the coding apparatuses shown in FIG. 1, the motion
compensation coding unit 107 determines, on a per-slice basis,
whether or not to code only the data concerning the parameter C (C1
and C2) corresponding to the DC components of image data, outputs
the information of the flag c_flag to the coded stream generation
unit 103 based on the determination, and describes the information
in the coded stream as shown in FIG. 17A. As a result, it is
possible to use all the weighting coefficient sets in a higher
performance apparatus for performing linear prediction, and to use
only the DC components in a lower performance apparatus for
performing linear prediction.
Similarly, in the coding apparatus as shown in FIG. 1, when linear
prediction is performed using fixed equations, the motion
compensation coding unit 107 determines, on a per-slice basis,
whether or not to perform coding by switching two equations,
outputs the information of the flag d_flag to the coded stream
generation unit 103 based on the determination, and describes the
information in the coded stream as shown in FIG. 17A. As a result,
it is possible to use either one of the fixed equations for linear
prediction in the case where there is little temporal change in
brightness of a picture, and to switch between the two fixed
equations for linear prediction in the case where the brightness of
the picture changes as time goes by.
Similarly, in the coding apparatus as shown in FIG. 1, the motion
compensation coding unit 107 determines, on a per-slice basis,
whether or not to generate coefficients for linear prediction using
the display order information of the reference pictures, outputs
the information of the flag t_flag to the coded stream generation
unit 103 based on the determination, and describes the information
in the coded stream as shown in FIG. 17A. As a result, it is
possible to code the weighting coefficient sets for linear
prediction in the case where there is enough space to be coded in
the coded stream, and to generate the coefficients from the display
order information for linear prediction in the case where there is
no more space to be coded.
Similarly, in the coding apparatus as shown in FIG. 1, the motion
compensation coding unit 107 determines, on a per-slice basis,
whether or not to approximate the coefficients for linear
prediction to the powers of 2 so as to allow the calculation of
these coefficients by shift operations, outputs the information of
the flag s_flag to the coded stream generation unit 103 based on
the determination, and describes the information in the coded
stream as shown in FIG. 17A. As a result, it is possible to use the
weighting coefficients without being approximated in a higher
performance apparatus for performing linear prediction, and to use
the weighting coefficients with being approximated to the powers of
2 in a lower performance apparatus for performing linear prediction
which can be realized only by shift operations.
For example, the case of (1) (p, c, d, t, s_flag)=(1, 0, 0, 0, 1)
shows that all the weighting coefficient sets are coded and linear
prediction is performed by only shift operations by representing
the coefficients as the powers of 2 as explained in the second
embodiment so as to generate a predictive image.
The case of (2) (p, c, d, t, s_flag)=(1, 1, 1, 0, 0) shows that
only the data concerning the parameter C (C1 and C2) is coded, the
method for generating a predictive image by adding the coefficient
C to the fixed equations as explained in the third embodiment is
used, and further the two fixed equations are switched for use.
In the case of (3) (p, c, d, t, s_flag)=(0, 0, 0, 0, 0), no
weighting coefficient set is coded. In other words, it shows that
the method for generating a predictive image using only the
equation 2b, out of the fixed equations in the conventional method,
is used.
The case of (4) (p, c, d, t, s_flag)=(0, 0, 1, 1, 1) shows that no
weighting coefficient set is coded, but the weighting coefficients
are generated from the display order information of the reference
pictures and linear prediction is performed by only shift
operations by approximating the generated coefficients to the
powers of 2, and then two fixed equations are switched for use so
as to generate a predictive image.
Note that in the present embodiment, the determinations are made
using five flags (p_flag, c_flag, d_flag, t_flag, s_flag), each of
which is 1 bit, but it is also possible to represent the
determinations with only one flag of 5 bits, instead of these five
flags. In that case, coding by use of variable length coding is
available, not by representation with 5 bits.
Note that in the present embodiment, all the five flags (p_flag,
c_flag, d_flag, t_flag, s_flag), each of which is 1 bit, are used,
but the same can be applied to the case where linear prediction
method is switched only using some of these flags. In that case,
the flags necessary for the linear prediction are only coded and
described, out of the flags as shown in FIG. 17A.
The conventional method allows switching, on a picture-by-picture
basis, between the predictive image generation method by use of
fixed equations and the predictive image generation method by use
of weighting coefficient sets of linear prediction coefficients, by
providing a flag for switching these methods in a picture common
information area in a coded stream. However, in the conventional
method, the predictive image generation method can only be switched
on a picture-by-picture basis.
As explained above, the present embodiment allows switching of the
predictive image generation method in each slice being a
subdivision of a picture by providing this switching flag in a
slice header in a coded stream. Therefore, it is possible to
generate a predictive image using the weighting coefficients in a
slice having complex images and to generate a predictive image
using fixed equations in a slice having simple images, and thus it
is possible to improve the image quality while minimizing the
increase in processing amount.
Note that in the present embodiment, five flags (p_flag, c_flag,
d_flag, t_flag, s_flag) are described in a slice header area for
determining whether the coefficients are coded or not for each
slice, but it is also possible to switch the determination on a
picture-by-picture basis by describing these flags in the picture
common information area. In addition, it is also possible to
generate a predictive image using the optimum method on a
block-by-block basis by providing the switching flag on each block
being a subdivision of a slice.
Note that the display order information in the present embodiment
is not limited to display order, but may be the actual display
time, or the order of respective pictures starting from a
predetermined picture, with its value increasing as the lapse of
display time.
Sixth Embodiment
FIG. 2 is a block diagram showing a structure of a moving picture
decoding apparatus in the sixth embodiment of the present
invention. Using this block diagram as shown in FIG. 2, the moving
picture decoding method executed by this moving picture decoding
apparatus will be explained in the following order: (1) an overview
of decoding and (2) a method for assigning reference indices, and
(3) a method for generating a predictive image. Here, it is assumed
that a coded stream which is generated by the moving picture coding
method in the first embodiment is inputted to the present decoding
apparatus.
(1) Overview of Decoding
First, the coded stream analysis unit 201 extracts the data
sequence of weighting coefficient sets for linear prediction and
the command sequence for assignment of reference indices from the
slice header area, and various information such as the reference
index information, the motion vector information and the coded
prediction error data from the coded block information area. FIG. 6
shows the above-mentioned various coded information in the coded
stream.
The data sequence of the weighting coefficient sets for linear
prediction extracted by the coded stream analysis unit 201 is
outputted to a linear prediction coefficient storage unit 206, the
command sequence for reference index assignment is outputted to a
reference index/picture number conversion unit 207, the reference
indices are outputted to a motion compensation decoding unit 204,
the motion vector information is outputted to a motion vector
storage unit 205, and the coded prediction error signal is
outputted to a prediction error decoding unit 202,
respectively.
The prediction error decoding unit 202 performs image decoding
processing such as inverse-quantization and inverse-frequency
transform for the inputted coded prediction error signal, and
outputs a decoded error signal. The addition unit 208 adds the
decoded prediction error signal and the predictive image signal
outputted from the motion compensation decoding unit 204 to
generate a reconstructed image signal. The obtained reconstructed
image signal is stored into a picture memory 203 for use for
reference in the following inter-picture prediction and output for
display.
The motion compensation decoding unit 204 extracts an image area
which is most suitable as a predictive image from the reconstructed
image signals stored in the picture memory 203, using the motion
vectors inputted from the motion vector storage unit 205 and the
reference indices inputted from the coded stream analysis unit 201.
At this time, the reference index/picture number conversion unit
207 designates the reference pictures in the picture memory 203
based on the correspondence between the reference indices given
from the coded stream analysis unit 201 and the picture
numbers.
The operation of the reference index/picture number conversion unit
207 will be explained in detail in the section (2). Further, the
motion compensation decoding unit 204 performs pixel value
conversion processing such as interpolation processing by linear
prediction on pixel values in the extracted image area, so as to
generate the final predictive image. The linear prediction
coefficients used for that processing are obtained from the data
stored in the linear prediction coefficient storage unit 206 using
the reference indices as search keys.
This predictive image generation method will be explained in detail
in the section (3).
The decoded image generated through the above-mentioned series of
processes is stored in the picture memory 203, and outputted as a
picture signal for display according to display timing.
The flow of operations in the case of inter-picture prediction
decoding has been described above, but a switch 209 switches
between inter-picture prediction decoding and intra-picture
prediction decoding. In the case of intra-picture decoding, a
predictive image is not generated by motion compensation, but a
decoded image is generated by generating a predictive image of a
current area to be decoded from a decoded area in the same picture
and adding the predictive image. The decoded image is stored in the
picture memory 203, as is the case with the inter-picture
prediction decoding, and outputted as a picture signal for display
according to display timing.
(2) Method for Assigning Reference Indices
Next, a method for assigning reference indices in the reference
index/picture number conversion unit 207 in FIG. 2 will be
explained using FIG. 3 and FIG. 4.
FIG. 3 is a diagram for explaining a method for assigning two
reference indices to picture numbers. When there is a sequence of
pictures ordered in display order, picture numbers are assigned in
decoding order. Commands for assigning the reference indices to the
picture numbers are described in a header of a slice that is a
subdivision of a picture, as the unit of decoding, and thus the
assignment thereof is updated every time one slice is decoded. The
command indicates, in series by the number of reference indices,
the differential value between a picture number which is assigned a
reference index currently and a picture number which is assigned a
reference index immediately before the current assignment.
Taking the first reference index in FIG. 3 as an example, since
"-1" is given as a command first, 1 is subtracted from the picture
number 16 of the current picture to be decoded and thus the
reference index 0 is assigned to the picture number 15. Next, since
"-4" is given, 4 is subtracted from the picture number 15 and thus
the reference index 1 is assigned to the picture number 11. The
following reference indices are assigned to respective picture
numbers in the same manner. The same applies to the second
reference indices.
According to the conventional reference index assignment method as
shown in FIG. 34, all the reference indices are corresponded to
respective picture numbers. On the other hand, in the example of
FIG. 3, the assignment method is exactly same as the conventional
method, but a plurality of reference indices are corresponded to
the same picture number by changing the values of the commands.
FIG. 4 shows the result of the assignment of the reference indices.
This diagram shows that the first reference indices and the second
reference indices are assigned to respective picture numbers
separately, but a plurality of reference indices are assigned to
one picture number in some cases. In the decoding method of the
present invention, it is assumed that a plurality of reference
indices are assigned to at least one picture number, like this
example.
If the reference indices are used only for determination of
reference pictures, the conventional method of one-to-one
assignment of reference indices to picture numbers is the most
efficient method. However, in the case where a weighting
coefficient set of linear prediction coefficients is selected for
generation of a predictive image using reference indices, the same
linear prediction coefficients have to be used for all the blocks
having the same reference pictures, so there is an extremely high
possibility that the optimum predictive image cannot be generated.
So, if it is possible to assign a plurality of reference indices to
one picture number as in the case of the present invention, the
optimum weighting coefficient set of linear prediction coefficients
can be selected from among a plurality of candidate sets for each
block even if all the blocks have the same reference picture, and
thus the predictive image with its prediction accuracy being higher
can be generated.
Note that, the above description shows the case where the picture
numbers are given assuming that all the reference pictures are
stored in a reference memory. However, since a current picture is
given a picture number which is larger by one than the number of a
picture which has been coded immediately before the current
picture, only when the current picture which has been coded lastly
is stored, so the continuity of the picture numbers are maintained
in the reference memory even if some pictures are not stored, and
thus the above-mentioned method can be used without change.
(3) Method for Generating Predictive Image
Next, the predictive image generation method in the motion
compensation decoding unit 204 in FIG. 2 will be explained using
FIG. 5. Although the predictive image generation method by linear
prediction is exactly the same as the conventional method,
flexibility in selection of linear prediction coefficients is
increased because a plurality of reference index numbers can be
corresponded to the same picture.
The picture B16 is a current B-picture to be decoded, and the
blocks BL01 and BL02 are current blocks to be decoded which belong
to the B-picture. The picture P11 and the picture B15 are used as
the first reference picture and the second reference picture for
BL01, and the predictive image is generated with reference to the
blocks BL11 and BL21 belonging to the pictures P11 and B15
respectively. In the same manner, the picture P11 and the picture
B15 are used as the first reference picture and the second
reference picture for BL02, and the predictive image is generated
with reference to the blocks BL12 and BL22 respectively.
Although both BL01 and BL02 refer to the same pictures as their
first reference picture and the second reference picture, it is
possible to assign different values to the first reference index
ref1 and the second reference index ref2 for BL01 and BL02
respectively by using the reference index assignment method as
explained in the above (2). Taking FIG. 4 as an example, 1 and 3
are assigned to the first reference index corresponding to the
picture number 11, whereas 1 and 6 are assigned to the second
reference index corresponding to the picture number 15. As a
result, four combinations of these reference indices, (ref1,
ref2)=(1, 1), (1, 6), (3, 1) and (3, 6) are supposed, and thus it
is possible to select the combination for deriving the optimum
weighting coefficient set on a per-block basis from among these
combinations. In FIG. 5, ref1=1 and ref2=1 are assigned for BL01,
and ref1=3 and ref2=6 are assigned for BL02, for example.
According to the conventional reference assignment method as shown
in FIG. 35, only one combination of (ref1, ref2)=(1, 1) can be
selected for both BL01 and BL02 in the case of FIG. 5, and thus
only one weighting coefficient set of linear prediction
coefficients can be selected, too. On the other hand, according to
the present invention, four options are available, and it can be
said that the possibility for selection of the optimum weighting
coefficient set is increased.
A coded stream of one picture is made up of a picture common
information area and a plurality of slice data areas. FIG. 6 shows
the structure of the slice data area in the coded stream. The slice
data area is further made up of a slice header area and a plurality
of block data areas. This diagram shows each block area
corresponding to BL01 and BL02 in FIG. 5 as an example of the block
data area.
"ref1" and "ref2" included in BL01 designate the first reference
index and the second reference index respectively indicating two
pictures referred to by the block BL01. Also, in the slice header
area, data for giving the weighting coefficient sets for the
above-mentioned linear prediction (pset0, pset1, pset2, . . . ) is
described for ref1 and ref2 respectively. In this area, "pset" s of
the number equivalent to the number of the reference indices as
explained in (2) can be set. To be more specific, in the case where
ten reference indices from 0 to 9 are used as each of the first
reference index and the second reference index, ten "pset" s from 0
to 9 can be set for each of ref1 and ref2.
FIG. 7 shows an example of tables of the weighting coefficient sets
included in the slice header area. Each data indicated by an
identifier pset has four values w1, w2, c and d, and these tables
are structured so that these values can be directly referred to by
the values of ref1 and ref2. Also, command sequences idx_cmd1 and
idx_cmd2 for assigning the reference indices to the picture numbers
are described in the slice header area.
Using ref1 and ref2 described in BL01 in FIG. 6, one set of
weighting coefficients is selected from each of the tables for ref1
and ref2 in FIG. 7. By performing linear prediction on the pixel
values of the reference images using these two sets of weighting
coefficients, a predictive image is generated.
Here, the flow of the processing from determination of weighting
coefficient sets until generation of a predictive image will be
explained.
FIG. 18 is a functional block diagram showing a functional
structure for generating a predictive image in the linear
prediction coefficient storage unit 206 and the motion compensation
decoding unit 204.
A predictive image is generated via the linear prediction
coefficient storage unit 206a, the linear prediction coefficient
storage unit 206b, the average calculation unit 204a and the linear
prediction operation unit 204b.
The average calculation unit 204a obtains, from the linear
prediction coefficient storage unit 206a, one set of weighting
coefficients (w1.sub.--1, w2.sub.--1, c.sub.--1, d.sub.--1)
selected by ref1 outputted from the coded stream analysis unit 201,
and obtains, from the linear prediction coefficient storage unit
206b, one set of weighting coefficients (w1.sub.--2, w2.sub.--2,
c.sub.--2, d.sub.--2) selected by ref2 outputted from the coded
stream analysis unit 201.
The average calculation unit 204a calculates the average, for
respective parameters, of the weighting coefficient sets obtained
from the linear prediction coefficient storage units 206a and 206b
respectively so as to output the averages to the linear prediction
operation unit 204b as the weighting coefficient set (w1, w2, c, d)
which is actually used for linear prediction. The linear prediction
operation unit 204b calculates the predictive image using the
equation 1 based on the weighting coefficient set (w1, w2, c, d)
for output.
FIG. 19 is a functional block diagram showing another functional
structure for generating a predictive image. A predictive image is
generated via the linear prediction coefficient storage unit 206a,
the linear prediction coefficient storage unit 206b, the linear
prediction operation unit 204c, the linear prediction operation
unit 204d and the average calculation unit 204e.
The linear prediction operation unit 204c obtains, from the linear
prediction coefficient storage unit 206a, one set of weighting
coefficients (w1.sub.--1, w2.sub.--1, c.sub.--1, d.sub.--1)
selected by ref1 outputted from the coded stream analysis unit 201,
and calculates the predictive image using the equation 1 based on
the weighting coefficient set for output to the average calculation
unit 204e.
In the same manner, the linear prediction operation unit 204d
obtains, from the linear prediction coefficient storage unit 206b,
one set of weighting coefficients (w1.sub.--2, w2.sub.--2,
c.sub.--2, d.sub.--2) selected by ref2 outputted from the coded
stream analysis unit 201, and calculates the predictive image using
the equation 1 based on the weighting coefficient set for output to
the average calculation unit 204e.
The average calculation unit 204e calculates the average, for
respective pixel values, of the predictive images which are
outputted from the linear prediction operation unit 204c and the
linear prediction operation unit 204d respectively so as to
generate the final predictive image for output.
FIG. 20A is a functional block diagram showing another functional
structure for generating a predictive image. A predictive image is
generated via the linear prediction coefficient storage unit 206c,
the linear prediction storage unit 206d, the average calculation
unit 204f, and the linear prediction operation unit 204g.
The average calculation unit 204f obtains, from the linear
prediction coefficient storage unit 206c, the parameters of
c.sub.--1 and d.sub.--1 in one set of weighting coefficients
(w1.sub.--1, w2.sub.--1, c.sub.--1, d.sub.--1) selected by ref1
outputted from the coded stream analysis unit 201, and similarly,
obtains, from the linear prediction coefficient storage unit 206d,
the parameters of c.sub.--2 and d.sub.--2 in one set of weighting
coefficients (w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2)
selected by ref2 outputted from the coded stream analysis unit 201.
The average calculation unit 204f calculates the average of
c.sub.--1 and c.sub.--2 and the average of d.sub.--1 and d.sub.--2
obtained from the linear prediction coefficient storage unit 206c
and the linear prediction coefficient storage unit 206d so as to
obtain c and d for output to the linear prediction operation unit
204g.
Also, the linear prediction operation unit 204g obtains the
parameter of w1.sub.--1 in the above-mentioned weighting
coefficient set (w1.sub.--1, w2.sub.--1, c.sub.--1, d.sub.--1) from
the linear prediction coefficient storage unit 206c, obtains the
parameter of w2.sub.--2 in the above-mentioned weighting
coefficient set (w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2) from
the linear prediction coefficient storage unit 206d, and obtains c
and d which are the averages calculated by the average calculation
unit 204f, and then calculates the predictive image using the
equation 1 for output.
To be more specific, when determining the weighting coefficient set
(w1, w2, c, d) which is actually used for linear prediction from
among the weighting coefficient set (w1.sub.--1, w2.sub.--1,
c.sub.--1, d.sub.--1) obtained from the linear prediction
coefficient storage unit 206c and the weighting coefficient set
(w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2) obtained from the
linear prediction coefficient storage unit 206d, the linear
prediction operation unit 204g uses the following rule.
w1=w1.sub.--1 w2=w2.sub.--2 c=(average of c.sub.--1 and c.sub.--2)
d=(average of d.sub.--1 and d.sub.--2)
FIG. 20B is a functional block diagram showing another functional
structure for generating a predictive image. A predictive image is
generated via the linear prediction coefficient storage unit 206e,
the linear prediction coefficient storage unit 206f and the linear
prediction operation unit 204h.
The linear prediction operation unit 204h obtains, from the linear
prediction coefficient storage unit 206e, the parameters of
w1.sub.--1, c.sub.--1 and d.sub.--1 which are a part of one set of
weighting coefficients (w1.sub.--1, w2.sub.--1, c.sub.--1,
d.sub.--1) selected by ref1 outputted from the coded stream
analysis unit 201, and similarly, obtains, from the linear
prediction coefficient storage unit 206f, the parameter of
w2.sub.--2 which is a part of one set of weighting coefficients
(w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2) selected by ref2
outputted from the coded stream analysis unit 201. The linear
prediction operation unit 204h calculates the predictive image
using the equation 1 based on w1.sub.--1, c.sub.--1, d.sub.--1,
w2.sub.--2 obtained from the linear prediction coefficient storage
unit 206e and the linear prediction coefficient storage unit 206f
for output.
To be more specific, when determining the weighting coefficient set
(w1, w2, c, d) which is actually used for linear prediction from
among the weighting coefficient set (w1.sub.--1, w2.sub.--1,
c.sub.--1, d.sub.--1) obtained from the linear prediction
coefficient storage unit 206e and the weighting coefficient set
(w1.sub.--2, w2.sub.--2, c.sub.--2, d.sub.--2) obtained from the
linear prediction coefficient storage unit 206f, the linear
prediction operation unit 204h uses the following rule.
w1=w1.sub.--1 w2=w2.sub.--2 c=c.sub.--1 d=d.sub.--1
Furthermore, it is possible to use one or more parameters out of
w1, w2, c and d as fixed values. FIG. 21 is a functional block
diagram in the case where only "d" is used as a fixed value for the
functional structure in FIG. 20A. A predictive image is generated
via the linear prediction coefficient storage unit 206g, the linear
prediction coefficient storage unit 206h, the average calculation
unit 204i and the linear prediction operation unit 204j.
The coefficients selected by the first reference index ref1 from
the linear prediction coefficient storage unit 206g are only
(w1.sub.--1, c.sub.--1), and the coefficients selected by the
second reference index ref 2 from the linear prediction coefficient
storage unit 206h are only (w2.sub.--2, c.sub.--2). The average
calculation unit 204i calculates the average of c.sub.--1and
c.sub.--2 obtained from the linear prediction coefficient storage
unit 206g and the linear prediction coefficient storage unit 206h
so as to obtain "c", and outputs it to the linear prediction
operation unit 204j.
The linear prediction operation unit 204j obtains the parameter of
w1.sub.--1 from the linear prediction coefficient storage unit
206g, obtains the parameter of w2.sub.--2 from the linear
prediction coefficient storage unit 206h, and obtains the parameter
of c from the average calculation unit 204i, and then calculates
the predictive image using a predetermined fixed value as a
parameter of d and the equation 1 for output. In this case, it is
also possible to modify the equation 1 into the equation 1b for use
as explained in the first embodiment.
It is possible to use one predetermined fixed value as a value of d
in any cases, but in the case where the coding apparatus describes
the above fixed value in the slice header, that fixed value can be
switched on a per-slice basis by extracting it in the coded stream
analysis unit 201. Similarly, the fixed value can be switched on a
per-picture basis or a per-sequence basis by describing it in the
picture common information area or the sequence common information
area.
Note that the above-mentioned decoding methods are concerned with a
B-picture having two reference pictures, but it is also possible to
execute the same processing in the single picture reference
decoding mode for a P-picture or a B-picture having only one
reference picture. In this case, using only one of the first
reference index and the second reference index, pset and idx_cmd
for either ref1 or ref2 are only described in the slice header area
included in the coded stream of FIG. 6, according to the reference
index described in the block data area. In addition, as a linear
prediction method, the following equation 3 or the equation 4 is
used instead of the equation 1 as explained in the conventional
method.
Use of the equation 1 and the equation 3 requires four parameters
w1, w2, c and d, but use of the equation 4 allows linear prediction
by use of only three parameters w1, c and d. In other words, it is
possible to reduce the number of data items of the weighting
coefficient set to be described in each slice header area to three,
when either one of the first reference index and the second
reference index is used for an entire picture like a P-picture.
If the equation 3 is used, it is possible to realize linear
prediction which is available for both B-pictures and P-pictures
adaptively without change in structure. If the equation 4 is used,
the data amount to be described in the header area of a P-picture
can be reduced, and thus it is possible to achieve reduction of
processing amount because of simplified calculation. However, since
the reference index assignment method suggested by the present
invention can directly be applied to any of the above methods, a
predictive image with higher prediction accuracy can be created,
which is extremely effective in image decoding.
By the way, the pictures which are referred to in motion
compensation are determined by designating the reference indices
assigned to respective pictures. In that case, the maximum number
of pictures which are available for reference has been described in
the picture common information area in the coded stream.
FIG. 38 is a schematic diagram of a coded stream in which the
maximum number of pictures which are available for reference is
described. As this diagram shows, the maximum number of pictures
for ref1 "Max_pic1" and the maximum number of pictures for ref2
"Max_pic2" are described in the picture common information in the
coded stream.
Information required for decoding is not the maximum number of real
pictures themselves, but the maximum reference index value
available for designating pictures.
Since one reference index is assigned to one picture in the
conventional method, above-mentioned description of the maximum
number of pictures causes no contradiction. But the difference in
number between reference indices and pictures has a significant
influence on the case where a plurality of reference indices are
assigned to one picture number, like the present invention.
As described above, command sequences idx_cmd1 and idx_cmd2 are
described in a coded stream in order to assign reference indices to
picture numbers. The picture numbers and the reference indices are
corresponded to each other based on each command in these command
sequences idx_cmd1 and idx_cmd2. For that purpose, knowing the
maximum reference index value shows that all the reference indices
and picture numbers have been corresponded to each other, namely,
the end of the commands in the command sequences idx_cmd1 and
idx_cmd2.
Therefore, in the present embodiment, the maximum number of
available reference indices, instead of the maximum number of
pictures in the background art, is described in the picture common
information area being a header of the picture. Or, both of the
maximum number of pictures and the maximum number of reference
indices are described.
FIG. 23 shows a picture common information area in a coded stream
of a picture in which the maximum number of reference indices is
described. In the picture common information area, the maximum
number of reference indices available for ref1 "Max_idx1" and the
maximum number of reference indices available for ref2 "Max_idx2"
are described.
In FIG. 23, the maximum number of reference indices is described in
the picture common information, but it may be structured so that
the maximum number of reference indices is described in the slice
data area as well as in the picture common information. For
example, the maximum number of reference indices required for each
slice can be clearly described, in the case where the maximum
number of required reference indices for each slice is
significantly different from the maximum number thereof described
in the picture common information area, from slice to slice, for
example, the maximum number of reference indices in a picture is 8,
the maximum number of reference indices required for the slice 1 in
the picture is 8, and the maximum number of reference indices
required for the slice 2 is 4.
In other words, it may be structured so that the maximum number of
reference indices described in the picture common information is
set to be the default value common to all the slices in the
picture, and the maximum number of reference indices required for
each slice, which is different from the default value, is described
in the slice header.
Although FIG. 23 and FIG. 38 show the examples where a coded stream
is made up of a picture common information area and slice data
areas, the picture common information area and the slice data areas
can be handled as separate coded streams in exactly the same manner
as one coded stream.
Seventh Embodiment
The moving picture decoding method in the seventh embodiment of the
present invention will be explained. Since the structure of the
decoding apparatus, the flow of decoding processing and the
reference index assignment method are exactly the same as the sixth
embodiment, the explanation thereof is not repeated here.
In the sixth embodiment, linear prediction is performed on each
pixel using the equation 1, the equation 3 or the equation 4 for
generating a predictive image in motion compensation. However,
since all of these equations include multiplications, which cause
significant increase in processing amount in considering that these
multiplications are performed on all the pixels.
So, it is possible to use the equation 5 instead of the equation 1,
the equation 6 instead of the equation 3, and the equation 7
instead of the equation 4. These equations allow calculations only
by bit shift operations without using multiplications, and thus
allows reduction of processing amount.
As is the case with the sixth embodiment, the equation 5 is used
for generating a predictive image with reference to two pictures at
a time, and the equation 6 or the equation 7 is used for generating
a predictive image with reference to only one picture. Since these
equations require identifiers indicating plus and minus signs,
weighting coefficient sets required for prediction operations are
(sign1, m, sign2, n, c) for the equations 5 and 6, and (sign1, m,
c) for the equation 7. "sing1" and "sign2" are parameters
identifying the first and second plus and minus signs,
respectively. Although the number of parameters is larger than that
in the third embodiment, there is little increase in processing
amount because both sign1 and sign2 can be represented by 1
bit.
Here, the flow of processing from determination of weighting
coefficient sets until generation of a predictive image with
reference to two pictures at a time using the equation 5 will be
explained in detail.
First, the case where the functional structure for generation of a
predictive image is that as shown in FIG. 18 will be explained. The
average calculation unit 204a obtains the weighting coefficient set
(sign1.sub.--1, m.sub.--1, sign2.sub.--1, n.sub.--1, c.sub.--1)
from the linear prediction coefficient storage unit 206a. Also, the
average calculation unit 204a obtains the weighting coefficient set
(sign1.sub.--2, m.sub.--2, sign2.sub.--2, n.sub.--2, c.sub.--2)
from the linear prediction coefficient storage unit 206b.
The average calculation unit 204a calculates, for respective
parameters, the average of the weighting coefficient sets obtained
from the linear prediction coefficient storage unit 206a and the
linear prediction coefficient storage unit 206b so as to consider
the average as the weighting coefficient set (sign1, m, sign2, n,
c). The linear prediction operation unit 204b calculates the
predictive image using the equation 5 based on the weighting
coefficient set (sign1, m, sign2, n, c) outputted from the average
calculation unit 204a.
Note that FIG. 18 shows the weighting coefficient set (w1.sub.--1,
w2.sub.--1, c.sub.--1, d.sub.--1) and the like obtained from the
linear prediction coefficient storage unit 206a and the like, which
are calculated in the case where the equation 1 is used as
explained in the sixth embodiment, and does not show the parameters
used in the case where the predictive image is obtained using the
equation 5, but the parameters used in the former case can be
replaced by the parameters in the latter case as they are. The same
goes for the cases of FIG. 19 and FIG. 20 to be described
later.
Next, the case where the functional structure for generation of a
predictive image is that as shown in FIG. 19 will be explained. The
linear prediction operation unit 204c calculates a predictive image
1 based on the weighting coefficient set (sign1.sub.--1, m.sub.--1,
sign2.sub.--1, n.sub.--1, c.sub.--1) obtained from the linear
prediction coefficient storage unit 206a. The linear prediction
operation unit 204d calculates a predictive image 2 based on the
weighting coefficient set (sign1.sub.--2, m.sub.--2, sign2.sub.--2,
n.sub.--2, c.sub.--2) obtained from the linear prediction
coefficient storage unit 206b. And the average calculation unit
204e calculates, for respective pixels, the average of the
predictive images calculated by the linear prediction operation
units 204c and 204d respectively so as to obtain a predictive
image.
In this case, the linear prediction operation unit 204c first
calculates the predictive image using the equation 5 based on the
weighting coefficient set (sign1.sub.--1, m.sub.--1, sign2.sub.--1,
n.sub.--1, c.sub.--1), so it is possible to calculate the
predictive image using bit shift operations without using
multiplications. The same goes for the linear prediction operation
unit 204d. On the other hand, in the case of FIG. 18, since the
average of the weighting coefficient set (sign1.sub.--1, m.sub.--1,
sign2.sub.--1, n.sub.--1, c.sub.--1) and the weighting coefficient
set (sign1.sub.--2, m.sub.--2, sign2.sub.--2, n.sub.--2, c.sub.--2)
is calculated first, the average of m.sub.--1 and m.sub.--2 or the
average of n.sub.--1 and n.sub.--2, namely, the exponents of 2,
could not be integers, and thus there is a possibility that the
processing amount increases. Also, if the exponents of 2 are
rounded off to integers, there is another possibility that the
error increases.
Next, the case where a predictive image is generated in the
functional structure as shown in FIG. 20A will be explained. The
linear prediction operation unit 204g calculates a predictive image
using the equation 5, based on the parameters sign1.sub.--1 and
m.sub.--1 which are obtained from the linear prediction coefficient
storage unit 206c and used for bit shift operations; the parameters
sign2.sub.--2 and n.sub.--2 which are obtained from the linear
prediction coefficient storage unit 206d and used for bit shift
operations; and the average c calculated by the average calculation
unit 204f, of the parameters c.sub.--1 and c.sub.--2 which are
obtained from the linear prediction coefficient storage units 206c
and 206d.
In this case, since the coefficients used for bit shift operations
are the values which are obtained directly from the linear
prediction coefficient storage unit 206c or the linear prediction
coefficient storage unit 206d, the exponents of 2 in the equation 5
are integers. Therefore, the calculations can be performed using
bit shift operations, and thus the processing amount can be
reduced.
The case where a predictive image is generated in the functional
structure as shown in FIG. 20B will be explained. The linear
prediction operation unit 204h calculates a predictive image using
the equation 5 based on the parameters sign1.sub.--1, m.sub.--1 and
c.sub.--1 which are obtained from the linear prediction coefficient
storage unit 206e and the parameters sign2.sub.--2 and n.sub.--2
which are obtained from the linear prediction coefficient storage
unit 206f.
In this case, since the coefficients used for bit shift operations
are values which are obtained directly from the linear prediction
coefficient storage unit 206e or the linear prediction coefficient
storage unit 206f, the exponents of 2 in the equation 5 are
integers. Therefore, the predictive image can be calculated using
bit shift operations, and thus the processing amount can be
reduced.
In the cases of FIGS. 20A and 20B, there are parameters which do
not need to be added to the coded stream for transmission, as is
the case with the cases of FIGS. 10A and 10B in the sixth
embodiment, and the data amount of the coded stream can be
reduced.
Using the linear prediction equations as explained in the seventh
embodiment, the calculations can be performed using bit shift
operations without using multiplications, so the processing amount
can be significantly reduced from that in the sixth embodiment.
In the present embodiment, linear prediction is performed using the
equations 5, 6 and 7 instead of the equations 1, 3 and 4, and using
the parameter set to be coded (sign1, m, sign2, n, c) instead of
(w1, w2, c, d), so the calculations can be realized only using bit
shift operations and thus reduction of processing amount is
achieved. However, it is also possible, as another approach, to use
the equations 1, 3 and 4 and (w1, w2, c, d) as they are, by
limiting the selectable values of w1 and w2 to only the values
available for bit shift operations, so the calculations can be
realized only using bit shift operations and thus reduction of
processing amount is achieved in exactly the same structure as that
in the sixth embodiment.
In addition, as a method for such limitation, it is possible to
limit the values of w1 and w2 so that 1 is always selected for such
values and input a coded stream having arbitrary values of only c1
and c2 which are DC components. Taking the structure of FIG. 21 as
an example, (1, c.sub.--1) for ref1 and (1, c.sub.--2) for ref2
shall be coded as parameter sets. In this case, the pixel value
P(i) of the predictive image is calculated by the following
equation in which w1.sub.--1 and w2.sub.--2 in the equation 1a are
substituted for 1. P(i)=(Q1(i)+Q2(i))/pow(2,
d)+(c.sub.--1+c.sub.--2)/2 (where pow(2, d) indicates the "d"th
power of 2)
Accordingly, it is possible to significantly reduce the processing
amount for linear prediction even in exactly the same structure as
that of the sixth embodiment.
In addition, as shown in FIG. 24, in the case where a flag sft_flg,
indicating whether it is possible or not to perform linear
prediction using only bit shift operations, and a flag dc_flg,
indicating whether it is possible or not to perform linear
prediction using only c that is a DC component, are described in
picture common information of a coded stream of a picture, the
decoding apparatus can perform decoding, referring to these flags,
in the structure suitable for linear prediction using only bit
shift operations or decoding in the structure suitable for linear
prediction using only a DC component. Accordingly, processing
amount can be reduced significantly depending on the structure of
the decoding apparatus.
Eighth Embodiment
The moving picture decoding method in the eighth embodiment of the
present invention will be explained. Since the structure of the
decoding apparatus, the flow of decoding processing and the
reference index assignment method are exactly same as those in the
sixth embodiment, the explanation thereof is not repeated here.
As explained in the background art, there is a method for
generating a predictive image using a predetermined fixed equation
such as the equation 2a and the equation 2b, unlike the sixth and
seventh embodiments in which a predictive image is generated using
a prediction equation obtained from weighting coefficient sets of
linear prediction coefficients. This conventional method has an
advantage that a data amount for coding can be reduced because
there is no need to code and transmit the weighting coefficient set
used for generating the predictive image. Also, the processing
amount for linear prediction can be significantly reduced because
the equations for linear prediction are simple. However, this
method using the fixed equations has a problem that prediction
accuracy is lowered because there are only two selectable linear
prediction equations 2a and 2b.
So, the equations 8a and 8b, instead of the equations 2a and 2b,
are used in the present embodiment. These equations 8a and 8b are
obtained by adding C1 and C2 to the equations 2a and 2b. Since only
the number of additions increases for the operation, there is
little increase in processing amount, compared with the original
equations 2a and 2b.
The equations 8a and 8b are prediction equations for generating a
predictive image with reference to two pictures at a time, but when
generating a predictive image with reference to only one picture,
the equation 9 is used instead of the equation 3 or 4 as explained
in the above embodiments.
The weighting coefficient sets for using this method are only (C1)
for ref1 and (C2) for ref2. Therefore, an example of a coded stream
of a picture obtained using this method is as shown in FIG. 14. In
the slice header area, the weighting coefficient sets for linear
prediction (pset0, pset1, pset2, . . . ) are described separately
for ref1 and ref2, and each of the weighting coefficient sets
includes only C. Similarly, FIG. 15 shows an example of weighting
coefficient sets included in the slice header area. Differently
from FIG. 7, each of the weighting coefficient sets in FIG. 15
includes only C.
FIG. 22 is a block diagram showing the functional structure for
generating a predictive image via the linear prediction coefficient
storage unit 206 and the motion compensation decoding unit 204 in
FIG. 2.
A predictive image is generated via the linear prediction
coefficient storage unit 206a, the linear prediction coefficient
storage unit 206b and the linear prediction operation unit
204a.
The weighting coefficient sets (C1) and (C2) having one element
respectively are obtained from the linear prediction coefficient
storage units 206a and 206b by the first reference index ref1 and
the second reference index ref2 outputted from the coded stream
analysis unit 201. These values are inputted to the linear
prediction operation unit 204a, where linear prediction is
performed on them using the equations 8a and 8b, and then the
predictive image is generated.
Similarly, when linear prediction is performed with reference to
only one picture, either one of the weighting coefficient sets (C1)
and (C2) is obtained using only one of ref1 and ref2 in FIG. 22,
linear prediction is performed using the equation 9, and then a
predictive image is generated.
Since the present embodiment requires only one parameter to be used
for each of ref1 and ref2, the data amount to be described in the
coded stream can be reduced. Also, since the linear prediction
equations do not require complex operations such as
multiplications, the operation amount can also be minimized. In
addition, the use of the coefficients C1 and C2 allows dramatic
improvement of the low prediction accuracy, which is considered as
a disadvantage of the conventional method of using fixed
equations.
Note that it is possible to use the linear prediction method as
explained in the present embodiment, regardless of whether a
plurality of reference indices can refer to the same picture or
not.
Ninth Embodiment
The moving picture decoding method in the ninth embodiment of the
present invention will be explained. Since the structure of the
decoding apparatus, the flow of decoding processing and the
reference index assignment method are exactly the same as the sixth
embodiment, the explanation thereof is not repeated here.
Display order information indicating display time or the
alternative thereto as well as a picture number are assigned to
each picture. FIG. 39 is a diagram showing an example of picture
numbers and the corresponding display order information. Certain
values are assigned to the display order information according to
display order. In this example, the value which increases one by
one for each picture is used. A method for generating values of
coefficients used in an equation for linear prediction using this
display order information will be explained in the ninth
embodiment.
In the sixth embodiment, linear prediction is performed for each
pixel using the equation 1, the equation 3 or the equation 4 when
generating a predictive image in motion compensation. However,
since the linear prediction requires data of coefficients, such
coefficient data is described in slice header areas in a coded
stream as weighting coefficient sets for use for creation of the
predictive image. Although this method achieves high coding
efficiency, it requires additional processing for creating data of
the weighting coefficient sets and causes increase in bit amount
because the weighting coefficient sets are described in the coded
stream.
So, it is also possible to perform linear prediction using the
equation 10, equation 11a or the equation 12a instead of the
equation 1. Using these equations, the weighting coefficients can
be determined based on only the display order information of each
reference picture, so there is no need to code the weighting
coefficient sets separately.
When it is assumed, as an example, that the current picture to be
decoded is No. 16, the picture designated by the first reference
index is No. 11, and the picture designated by the second reference
index is No. 10, the display order information of respective
pictures are 15, 13 and 10, and thus the following linear
prediction equations are determined. V1=(10-15)/(10-13)=5/3
V2=(15-13)/(10-13)=-2/3 P(i)=5/3.times.Q1(i)-2/3.times.Q2(i)
Compared with the method for performing linear prediction using
weighting coefficient sets in the equation 1, the above equations
have lower flexibility of coefficient values, and thus it can be
said that it is impossible to create the optimum predictive image.
However, compared with the method of switching the two fixed
equations 2a and 2b depending on the positional relationship
between two reference pictures, the above equations are more
efficient linear prediction equations.
When both the first reference index and the second reference index
referto the same picture, the equation 11a and the equation 12a do
not hold because T1 becomes equal to T2. So, when the two reference
pictures have the same display order information, linear prediction
shall be performed using 1/2 as the values of V1 and V2. In that
case, the linear prediction equations are as follows. V1=1/2 V2=1/2
P(i)=1/2.times.Q1(i)+1/2.times.Q2(i)
Also, the equations 11a and 12a do not hold because T1 becomes
equal to T2 when the first reference index and the second reference
index refer to difference pictures but these pictures have the same
display order information. When the two reference pictures have the
same display order information as mentioned above, linear
prediction shall be performed using 1/2 as the values of V1 and
V2.
As described above, when two reference pictures have the same
display order information, it is possible to use a predetermined
value as a coefficient. Such predetermined coefficient may be one
having the same weight like 1/2 as shown in the above example.
By the way, use of the equation 10 in the present embodiment
requires multiplications and divisions for linear prediction. Since
the linear prediction operation using the equation 10 is the
operation on all the pixels in a current block to be decoded,
addition of multiplications causes significant increase in the
processing amount.
So, approximation of V1 and V2 to the powers of 2 like the case of
the seventh embodiment makes it possible to perform linear
prediction operation by only shift operations, and thus to achieve
reduction of the processing amount. As the linear prediction
equations for that case, the equations 11b and 12b are used instead
of the equations 11a and 12a.
Note that it is also possible to use the equations 11c and 12c
instead of the equations 11a and 12a.
Note that it is also possible to use the equations 11d and 12d
instead of the equations 11a and 12a.
Note that the value of V1 and V2 approximated to the power of 2
shall be, taking the equation 11b as an example, the value of
.+-.pow(2, v1) obtained when the values of .+-.pow(2, v1) and
(T2-T0)/(T2-T1) are mostly approximated to each other as the value
of v1 changes one by one.
For example, in FIG. 39, when a current picture to be decoded is
No. 16, the picture designated by the first reference index is No.
11, and the picture designated by the second reference index is No.
10, the display order information of the respective pictures are
15, 13 and 10, so (T2-T0)/(T2-T1) and .+-.pow(2, v1) are as
follows. (T2-T0)/(T2-T1)=(10-15)/(10-13)=5/3 +pow(2, 0)=1 +pow(2,
1)=2
Since 5/3 is close to 2 rather than 1, V=2 is obtained as a result
of approximation.
As another method of approximation, it is also possible to switch
between round-up approximation and round-down approximation
depending on the relationship between two values of display order
information T1 and T2.
In that case, round-up approximation is performed on both V1 and V2
when T1 is later than T2, and round-down approximation is performed
on both V1 and V2 when T1 is earlier than T2. It is also possible,
in a reverse manner, to perform round-down approximation on both V1
and V2 when T1 is later than T2, and round-up approximation on both
V1 and V2 when T1 is earlier than T2.
As another approximation method using display order information,
round-up approximation is performed in an equation for V1 and
round-down approximation is performed in an equation for V2 when T1
is later than T2. As a result, the difference between the values of
the two coefficients becomes large, so it is likely that values
suitable for extrapolation are obtained. On the contrary, when T1
is earlier than T2, the value in the equation for V1 and the value
in the equation for V2 are compared, and then round-up
approximation is performed on the smaller value and round-down
approximation is performed on the larger value. As a result, the
difference between the values of the two coefficients becomes
small, so it is likely that values suitable for interpolation are
obtained.
For example, in FIG. 39, when a current picture to be decoded is
No. 16, the picture designated by the first reference index is No.
11, and the picture designated by the second reference index is No.
10, the display order information of the respective pictures are
15, 13 and 10. Since T1 is later than T2, round-up approximation is
performed on the equation for V1 and round-down approximation is
performed on the equation for V2. As a result, the equations 11b
and 12b are calculated as follows.
(T2-T0)/(T2-T1)=(10-15)/(10-13)=5/3 +pow(2, 0)=1 +pow(2, 1)=2 (1)
Equation 11b
As a result of round-up approximation, V1=2 is obtained.
(T0-T1)/(T2-T1)=(15-13)/(10-13)=-2/3 -pow(2, 0)=-1 -pow(2, -1)=-1/2
(2) Equation 12b
As a result of round-down approximation, V2=-1 is obtained.
Note that although the equation 10 is only one equation for liner
prediction in the above embodiments, it is also possible to combine
this method with the linear prediction method by use of two fixed
equations 2a and 2b as explained in the background art. In that
case, the equation 10 is used instead of the equation 2a, and the
equation 2b is used as it is. To be more specific, the equation 10
is used when the picture designated by the first reference index
appears behind the picture designated by the second reference index
in display order, whereas the equation 2b is used in other
cases.
It is also possible, on the contrary, to use the equation 10
instead of the equation 2b and use the equation 2a as it is. To be
more specific, the equation 2a is used when the picture designated
by the first reference index appears behind the picture designated
by the second reference index, and the equation 10 is used in other
cases. However, when the two reference pictures have the same
display order information, linear prediction is performed using 1/2
as the values of V1 and V2.
It is also possible to describe only the coefficient C in the slice
header areas to be used for linear prediction, in the same manner
as the concept of the eighth embodiment. In that case, the equation
13 is used instead of the equation 10. V1 and V2 are obtained in
the same manner as the above embodiments.
The processing for generating coefficients is needed, and further
the coefficient data needs to be decoded into the slice header
area, but use of C1 and C2 allows more accurate linear prediction
even if the accuracy of V1 and V2 is low. This is effective
particularly in the case where V1 and V2 are approximated to the
powers of 2 for linear prediction.
Note that using the equation 13, the linear prediction can be
performed in the same manner in both cases where one reference
index is assigned to one picture and a plurality of reference
indices are assigned to one picture.
In the calculation of the values in each of the equations 11a, 12a,
11b, 12b, 11c, 12c, 11d and 12d, the combinations of available
values are limited to some extent in every slice. So, only one
operation is enough for decoding a slice, unlike the equation 10 or
the equation 13 in which the operation needs to be performed for
all the pixels in a current block to be decoded, and thus there
seems to be little influence on the entire processing amount.
Note that the display order information in the present embodiment
is not limited to display order, but may be the actual display
time, or the order of respective pictures starting from a
predetermined picture, with its value increasing as the lapse of
display time.
Tenth Embodiment
The moving picture decoding method in the tenth embodiment of the
present invention will be explained. Since the structure of the
decoding apparatus, the flow of decoding processing and the
reference index assignment method are exactly same as the sixth
embodiment, the explanation thereof is not repeated here.
In the conventional method, it is possible to switch, if necessary,
between generation of a predictive image by use of fixed equations
and generation of a predictive image by use of weighting
coefficient sets of linear prediction coefficients, using flags
described in a picture common information area in a coded
stream.
In the present embodiment, another method for switching the various
linear prediction methods as explained in the above sixth to ninth
embodiments using flags will be explained.
FIG. 17A shows the structure used for the case where five flags
(p_flag, c_flag, d_flag, t_flag, s_flag) for controlling the above
switching are described in the slice header area in the coded
stream.
As shown in FIG. 17B, p_flag is a flag indicating whether weighting
coefficients have been coded or not. c_flag is a flag indicating
whether only the data of the parameter C (C1 and C2), out of the
parameters for ref1 and ref2, has been coded or not. t_flag is a
flag indicating whether weighting coefficients for linear
prediction are to be generated or not using the display order
information of the reference pictures. And s_flag is a flag
indicating whether the weighting coefficients for linear prediction
are to be approximated to the powers of 2 or not for the
calculation by use of shift operations.
Furthermore, d_flag is a flag indicating whether or not to switch
two predetermined fixed equations like the equations 2a and 2b
depending on the temporal positional relationship between the
picture designated by ref1 and the picture designated by ref2, when
linear prediction is performed using such two fixed equations. To
be more specific, when this flag indicates the switching of the
equations, the equation 2a is used in the case where the picture
designated by ref1 is later than the picture designated by ref2 in
display order and the equation 2b is used in other cases for
performing linear prediction, as is the case with the conventional
method. On the other hand, when this flag indicates no switching of
the equations, the equation 2b is always used for linear
prediction, regardless of the positional relationship between the
picture designated by ref1 and the picture designated by ref2.
Note that even if the equation 2a is used instead of the equation
2b as an equation to be used without switching, the equation 2a can
be handled in the same manner as the equation 2b.
In the decoding apparatus as shown in FIG. 2, the coded stream
analysis unit 201 analyzes the value of the flag p_flag, and
outputs, to the motion compensation decoding unit 204, the
instruction indicating whether or not to decode the data concerning
the weighting coefficient sets so as to generate a predictive image
based on the result of the analysis, and then the motion
compensation decoding unit 204 performs motion compensation by
linear prediction. As a result, it is possible to use the weighting
coefficient sets in a higher performance apparatus for performing
linear prediction, and not to use the weighting coefficient sets in
a lower performance apparatus for performing linear prediction.
Similarly, in the decoding apparatus as shown in FIG. 2, the coded
stream analysis unit 201 analyzes the value of the flag c_flag, and
outputs, to the motion compensation decoding unit 204, the
instruction indicating whether or not to decode only the data
concerning the parameter C (C1 and C2) corresponding to the DC
components of image data so as to generate a predictive image by
use of fixed equations, based on the result of the analysis, and
then the motion compensation decoding unit 204 performs motion
compensation by linear prediction. As a result, it is possible to
use the weighting coefficient sets in a higher performance
apparatus for performing linear prediction, and to use only the DC
components in a lower performance apparatus for performing linear
prediction.
Similarly, in the decoding apparatus as shown in FIG. 2, when the
coded stream analysis unit 201 analyzes the value of the flag
d_flag and linear prediction is performed using fixed equations
based on the result of the analysis, the coded stream analysis unit
201 outputs the instruction indicating whether or not to switch two
equations for decoding to the motion compensation decoding unit
204, in which motion compensation is performed. As a result, it is
possible to switch the method, such that either one of the fixed
equations is used for linear prediction in the case where there is
little temporal change in brightness of a picture, and the two
fixed equations are switched for linear prediction in the case
where the brightness of the picture changes as time goes by.
Similarly, in the decoding apparatus as shown in FIG. 2, the coded
stream analysis unit 201 analyzes the value of the flag t_flag and
based on the result of the analysis, it outputs, to the motion
compensation decoding unit 204, the instruction indicating whether
or not to generate the coefficients for linear prediction using the
display order information of the reference pictures, and the motion
compensation decoding unit 204 performs motion compensation. As a
result, it is possible for the coding apparatus to code the
weighting coefficient sets for linear prediction in the case where
more coding can be done, and to generate the coefficients from the
display order information for linear prediction in the case where
no more coding can be done.
Similarly, in the coding apparatus as shown in FIG. 2, the coded
stream analysis unit 201 analyzes the value of the flag s_flag, and
based on the result of the analysis, it outputs, to the motion
compensation decoding unit 204, the instruction indicating whether
or not to approximate the coefficients for linear prediction to the
powers of 2 so as to allow the calculation of these coefficients by
shift operations, and the motion compensation decoding unit 204
performs motion compensation. As a result, it is possible to use
the weighting coefficients without being approximated in a higher
performance apparatus for performing linear prediction, and to use
the weighting coefficients with being approximated to the powers of
2 in a lower performance apparatus for performing linear prediction
which can be realized by shift operations.
For example, the case of (1) (p, c, d, t, s_flag)=(1, 0, 0, 0, 1)
shows that all the weighting coefficient sets are decoded and
linear prediction is performed by only shift operations by
representing the coefficients as the powers of 2 as explained in
the seventh embodiment, so as to generate a predictive image.
The case of (2) (p, c, d, t, s_flag)=(1, 1, 1, 0, 0) shows that
only the data concerning the parameter C (C1 and C2) is decoded,
the method for generating a predictive image by adding the
coefficient C to the fixed equations as explained in the eighth
embodiment is used, and further the two fixed equations are
switched for use.
In the case of (3) (p, c, d, t, s_flag)=(0, 0, 0, 0, 0), no
weighting coefficient set is decoded. In other words, it shows that
the method for generating a predictive image using only the
equation 2b, out of the fixed equations as the conventional method,
is used.
The case of (4) (p, c, d, t, s_flag)=(0, 0, 1, 1, 1) shows that no
weighting coefficient set is decoded, but linear prediction is
performed by only shift operations by generating the weighting
coefficients from the display order information of the reference
pictures and further approximating the coefficients to the powers
of 2, as explained in the ninth embodiment, and then the two fixed
equations are switched for use, so as to generate a predictive
image.
Note that in the present embodiment, the determinations are made
using five flags (p_flag, c_flag, d_flag, t_flag, s_flag), each of
which is 1 bit, but it is also possible to represent the
determinations with only one flag of 5 bits, instead of these five
flags. In that case, decoding by use of variable length decoding is
available, not by representation with 5 bits.
Note that in the present embodiment, all the five flags (p_flag,
c_flag, d_flag, t_flag, s_flag), each of which is 1 bit, are used,
but the same can be applied to the case where linear prediction
method is switched only using some of these flags. In that case,
the flags necessary for the linear prediction are only coded and
described, out of the flags as shown in FIG. 17A.
In the conventional method, a flag is provided in a picture common
information area of a coded stream for switching between generation
of a predictive image by use of fixed equations and generation of a
predictive image by use of weighting coefficient sets of linear
prediction coefficients, so as to allow the switching between them
on a picture-by-picture basis. However, in this method, the
predictive image generation method can only be switched on a
picture-by-picture basis.
On the contrary, in the present embodiment as mentioned above, it
is possible to switch the method for generating a predictive image
for each slice that is a subdivision of a picture by providing the
switching flag in a slice header of a coded stream. Therefore, it
is possible, for example, to generate the predictive image by use
of the weighting coefficient sets in a slice containing complex
images, whereas to generate the predictive image by use of the
fixed equations in a slice containing simple images. As a result,
the image quality can be improved while minimizing the increase in
processing amount.
Note that in the present embodiment, five flags (p_flag, c_flag,
d_flag, t_flag, s_flag) are described in a slice header area for
the determination of the method in each slice, but it is also
possible to switch the determination on a picture-by-picture basis
by describing these flags in the picture common information area.
In addition, it is also possible to generate a predictive image by
the optimum method on a block-by-block basis by providing the
switching flag on each block being a subdivision of a slice.
Note that the display order information in the present embodiment
is not limited to display order, but may be the actual display
time, or the order of respective pictures starting from a
predetermined picture, with its value increasing as the lapse of
display time.
Eleventh Embodiment
The moving picture coding method and the moving picture decoding
method in the eleventh embodiment of the present invention will be
explained. Since the structures of the coding apparatus and the
decoding apparatus, the flows of coding processing and decoding
processing, and the reference index assignment method are exactly
the same as those in the first and sixth embodiments, the
explanation thereof is not repeated here.
In the present embodiment, the technology which is similar to that
explained in the fifth and tenth embodiments will be explained.
The flag p_flag indicating whether a parameter set is coded or not
and the flag c_flag indicating whether only the data concerning the
parameter C (C1 and C2) is coded or not, out of the parameters for
ref1 and ref2, are described in each slice.
In the coding apparatus as shown in FIG. 1, the motion compensation
coding unit 107 determines, on a slice-by-slice basis or a
block-by-block basis, whether or not to code the data concerning
the parameter set, and outputs, based on the determination, the
information of the flag p_flag to the coded stream generation unit
103, in which that information is described into the coded stream,
as shown in FIG. 40A.
Similarly, in the coded apparatus as shown in FIG. 1, the motion
compensation coding unit 107 determines, on a slice-by-slice basis
or a block-by-block basis, whether or not to code only the data
concerning the parameter C (C1 and C2) corresponding to the DC
components of image data, and outputs, based on the determination,
the information of the flag c_flag to the coded stream generation
unit 103, in which the information is described into the coded
stream, as shown in FIG. 40A.
On the other hand, in the decoding apparatus as shown in FIG. 2,
the coded stream analysis unit 201 analyzes the values of the
switching flags p_flag and c_flag, and based on the analysis,
outputs, to the motion compensation decoding unit 204, the
instruction indicating whether to generate a predictive image by
use of the downloaded parameter sets, or to generate a predictive
image by use of fixed equations, for example, and the motion
compensation decoding unit 204 performs motion compensation by
linear prediction.
For example, as shown in FIG. 40B, (1) when the flag p_flag is 1
and the flag c_flag is 0, the coding apparatus codes all the
parameter sets, (2) when the flag p_flag is 1 and the flag c_flag
is 1, the coding apparatus codes only the data concerning the
parameter C (C1 and C2), and further (3) when the flag p_flag is 0
and the flag c_flag is 0, the coding apparatus does not code any
parameter sets. Note that by determining the flag values as shown
in FIG. 40B, it can be found whether the DC component of the image
data has been coded or not using the value of the flag p_flag.
The coding apparatus processes the parameters as explained in FIG.
8 to FIG. 10, for example, in the above case (1). It processes the
parameters as explained in FIG. 16, for example, in the above case
(2). It processes the parameters using fixed equations, for
example, in the above case (3).
The decoding apparatus processes the parameters as explained in
FIG. 18 to FIG. 20, for example, in the above case (1). It
processes the parameters as explained in FIG. 22, for example, in
the above case (2). It processes the parameters using fixed
equations, for example, in the above case (3).
Another example of a combination of the above cases (1) to (3) will
be explained specifically.
In the above example, coding of parameters (whether or not to have
the decoding apparatus receive the parameters) is switched
explicitly using the flags p_flag and c_flag, but it is also
possible to use a variable length coding table (VLC table) instead
of the above flags.
As shown in FIGS. 41A and 41B, it is also possible to select
explicitly whether to switch between the fixed equation 2a and the
fixed equation 2b.
Here, no switching of the equation 2 means the following. It is
explained in the background art, for example, that, in order to
generate a predictive image, the fixed equation 2a including fixed
coefficients is selected when the picture designated by the first
reference index appears behind in display order the picture
designated by the second reference index, and the equation 2b
including fixed coefficients is selected in other cases. On the
other hands, when it is instructed, as shown in the example of FIG.
41B, not to switch the equation, it means that the fixed equation
2b including fixed coefficients is selected even when the picture
designated by the first reference index appears behind in coding
order the picture designated by the second reference index so as to
generate a predictive image.
The information of the flag v_flag for selecting explicitly whether
to switch between the fixed equation 2a and the fixed equation 2b
is outputted from the coded stream generation unit 103 and
described in the coded stream as shown in FIG. 41A.
FIG. 41B shows an example of processing by use of the flag v_flag.
As shown in FIG. 41B, when the flag v_flag is 1, the parameters are
not coded (the parameters are not downloaded on the decoding
apparatus. The same goes for the following.), and the fixed
equation 2 is not switched. When the flag v_flag is 01, the
parameters are not coded, and the fixed equation 2 is switched.
When the flag v_flag is 0000, only the parameter C is coded, and
the equation 2 is not switched.
Further, when the flag v_flag is 0001, only the parameter C is
coded, and the equation 2 is switched. When the flag v_flag is
0010, all the parameters are coded, and the equation 2 is not
switched. When the flag v_flag is 0011, all the parameters are
coded, and the fixed equation 2 is switched.
Note that since all the parameters are coded when v_flag is 0010
and 0011, it is possible to perform linear prediction using
weighting parameters, without using fixed equations, and in that
case, the determination of whether to switch the fixed equation or
not for use is ignored.
Note that the flag v_flag can be switched by the motion
compensation coding unit 107 in the coding apparatus as shown in
FIG. 1 and the motion compensation decoding unit 204 in the
decoding apparatus as shown in FIG. 2. It is also possible to use
the flag d_flag indicating whether to switch the fixed equation or
not, instead of the flag v_flag, in addition to the above flags
p_flag and c_flag.
As described above, use of flags allows switching of whether or not
the decoding apparatus receives (downloads) coded parameters after
the coding apparatus codes the parameters. As a result, the
parameters to be coded (or received) can be switched explicitly
according to the characteristics of the application and the
performance of the decoding apparatus.
In addition, since the fixed equation can be switched explicitly,
the variety of means for improving the image quality is increased,
and thus the coding efficiency is also improved. Also, even if the
decoding apparatus does not have a fixed equation, it can switch to
the fixed equation explicitly, and thus generate a predictive image
using the explicitly selected fixed equation.
Note that the placement of the flags is not limited to that as
shown in FIG. 40. Also, the values of the flags are not limited to
those as explained above. Furthermore, since four types of uses of
parameters can be explicitly shown using two types of flags, the
parameters may be assigned in the manners other than those as
explained above. In addition, all the parameters are transmitted in
the above example, but all the necessary parameter sets may be
transmitted, as explained in FIG. 10 and FIG. 20, for example.
Twelfth Embodiment
If a program for realizing the structures of the picture coding
method or the picture decoding method as shown in each of the above
embodiments is recorded on a memory medium such as a flexible disk,
it becomes possible to perform the processing as shown in each of
the embodiments easily in an independent computer system.
FIGS. 25A, 25B and 25C are illustrations showing the case where the
processing is performed in a computer system using a flexible disk
which stores the picture coding method or the picture decoding
method of the above first to eleventh embodiments.
FIG. 25B shows a front view and a cross-sectional view of an
appearance of a flexible disk, and the flexible disk itself, and
FIG. 25A shows an example of a physical format of a flexible disk
as a recording medium body. The flexible disk FD is contained in a
case F, and a plurality of tracks Tr are formed concentrically on
the surface of the disk in the radius direction from the periphery
and each track is divided into 16 sectors Se in the angular
direction. Therefore, as for the flexible disk storing the
above-mentioned program, the picture coding method as the program
is recorded in an area allocated for it on the flexible disk
FD.
FIG. 25C shows the structure for recording and reproducing the
program on and from the flexible disk FD. When the program is
recorded on the flexible disk FD, the picture coding method or the
picture decoding method as a program is written in the flexible
disk from the computer system Cs via a flexible disk drive. When
the picture coding method is constructed in the computer system by
the program on the flexible disk, the program is read out from the
flexible disk using the flexible disk drive and transferred to the
computer system.
The above explanation is made on the assumption that a recording
medium is a flexible disk, but the same processing can also be
performed using an optical disk. In addition, the recording medium
is not limited to a flexible disk and an optical disk, but any
other medium such as an IC card and a ROM cassette capable of
recording a program can be used.
Thirteenth Embodiment
FIG. 26.about.FIG. 29 are illustrations of devices for performing
the coding processing or the decoding processing as described in
the above embodiments and a system using them.
FIG. 26 is a block diagram showing the overall configuration of a
content supply system ex100 for realizing content distribution
service. The area for providing communication service is divided
into cells of desired size, and base stations ex107 to ex110 which
are fixed wireless stations are placed in respective cells.
In this content supply system ex100, devices such as a computer
ex111l, a personal digital assistant (PDA) ex112, a camera ex113, a
mobile phone ex114 and a camera-equipped mobile phone ex115 are
connected to the Internet ex 101 via an Internet service provider
ex102, a telephone network ex104 and base stations ex107 to
ex110.
However, the content supply system ex100 is not limited to the
configuration as shown in FIG. 26, and a combination of any of them
may be connected. Also, each device may be connected directly to
the telephone network ex104, not through the base stations ex107 to
ex110.
The camera ex113 is a device such as a digital video camera capable
of shooting moving pictures. The mobile phone may be a mobile phone
of a personal digital communications (PDC) system, a code division
multiple access (CDMA) system, a wideband-code division multiple
access (W-CDMA) system or a global system for mobile communications
(GSM) system, a personal handyphone system (PHS), or the like.
A streaming server ex103 is connected to the camera ex113 via the
base station ex109 and the telephone network ex104, which allows
live distribution or the like using the camera ex113 based on the
coded data transmitted from a user. Either the camera ex113 or the
server for transmitting the data may code the data.
Also, the moving picture data shot by a camera ex116 may be
transmitted to the streaming server ex103 via the computer ex111.
The camera ex116 is a device such as a digital camera capable of
shooting still and moving pictures. Either the camera ex116 or the
computer ex111 may code the moving picture data. An LSI ex117
included in the computer ex111 or the camera ex116 actually
performs coding processing.
Software for coding and decoding moving pictures may be integrated
into any type of a storage medium (such as a CD-ROM, a flexible
disk and a hard disk) being a recording medium which is readable by
the computer exll or the like. Furthermore, a camera-equipped
mobile phone ex115 may transmit the moving picture data. This
moving picture data is the data coded by the LSI included in the
mobile phone ex115.
The content supply system ex100 codes contents (such as video of
live music performance) shot by users using the camera ex113, the
camera ex116 or the like in the same manner as the above
embodiments and transmits them to the streaming server ex103, while
the streaming server ex103 makes stream distribution of the content
data to the clients at their request. The clients include the
computer ex111, the PDA ex112, the camera ex113, the mobile phone
ex114 and so on capable of decoding the above-mentioned coded data.
In the content supply system ex100, the clients can thus receive
and reproduce the coded data, and further the clients can receive,
decode and reproduce the data in real time so as to realize
personal broadcasting.
When each device in this system performs coding or decoding, the
moving picture coding apparatus or the moving picture decoding
apparatus, as shown in each of the above-mentioned embodiments, can
be used.
A mobile phone will be explained as an example of the device.
FIG. 27 is a diagram showing the mobile phone ex115 that uses the
moving picture coding method and the moving picture decoding method
explained in the above embodiments. The mobile phone ex115 has an
antenna ex201 for sending and receiving radio waves to and from the
base station ex110, a camera unit ex203 such as a CCD camera
capable of shooting video and still pictures, a display unit ex202
such as a liquid crystal display for displaying the data obtained
by decoding video and the like shot by the camera unit ex203 and
received via the antenna ex201, a body unit including a set of
operation keys ex204, a voice output unit ex208 such as a speaker
for outputting voices, a voice input unit 205 such as a microphone
for inputting voices, a storage medium ex207 for storing coded or
decoded data such as data of moving or still pictures shot by the
camera, and text data and data of moving or still pictures of
received e-mails, and a slot unit ex206 for attaching the storage
medium ex207 to the mobile phone ex115. The storage medium ex207
includes a flash memory element, a kind of an electrically erasable
and programmable read only memory (EEPROM) that is an electrically
erasable and rewritable nonvolatile memory, in a plastic case such
as an SD card.
The mobile phone ex115 will be further explained with reference to
FIG. 28. In the mobile phone ex115, a power supply circuit unit
ex310, an operation input control unit ex304, a picture coding unit
ex312, a camera interface unit ex303, a liquid crystal display
(LCD) control unit ex302, a picture decoding unit ex309, a
multiplex/demultiplex unit ex308, a record/reproduce unit ex307, a
modem circuit unit ex3O6 and a voice processing unit ex305 are
connected to a main control unit ex311 structured for overall
controlling the display unit ex202 and the body unit including the
operation keys ex204, and they are connected to each other via a
synchronous bus ex313.
When a call-end key or a power key is turned ON by a user's
operation, the power supply circuit unit ex310 supplies respective
units with power from a battery pack so as to activate the
camera-equipped digital mobile phone ex115 for making it into a
ready state.
In the mobile phone ex115, the voice processing unit ex305 converts
the voice signals received by the voice input unit ex205 in
conversation mode into digital voice data under the control of the
main control unit ex311 including a CPU, ROM, RAM and others, the
modem circuit unit ex306 performs spread spectrum processing of the
digital voice data, and the send/receive circuit unit ex301
performs digital-to-analog conversion and frequency transform of
the data, so as to transmit it via the antenna ex201. Also, in the
mobile phone ex115, after the data received by the antenna ex201 in
conversation mode is amplified and performed of frequency transform
and analog-to-digital conversion, the modem circuit unit ex306
performs inverse spread spectrum processing of the data, and the
voice processing unit ex305 converts it into analog voice data, so
as to output it via the voice output unit 208.
Furthermore, when transmitting e-mail in data communication mode,
the text data of the e-mail inputted by operating the operation
keys ex204 on the body unit is sent out to the main control unit
ex311 via the operation input control unit ex304. In the main
control unit ex311, after the modem circuit unit ex306 performs
spread spectrum processing of the text data and the send/receive
circuit unit ex301 performs digital-to-analog conversion and
frequency transform for it, the data is transmitted to the base
station ex110 via the antenna ex201.
When picture data is transmitted in data communication mode, the
picture data shot by the camera unit ex203 is supplied to the
picture coding unit ex312 via the camera interface unit ex303. When
the picture data is not transmitted, it is also possible to display
the picture data shot by the camera unit ex203 directly on the
display unit 202 via the camera interface unit ex303 and the LCD
control unit ex302.
The picture coding unit ex312, which includes the picture coding
apparatus as explained in the present invention, compresses and
codes the picture data supplied from the camera unit ex203 by the
coding method used for the picture coding apparatus as shown in the
above embodiments so as to transform it into coded picture data,
and sends it out to the multiplex/demultiplex unit ex308. At this
time, the mobile phone ex115 sends out the voices received by the
voice input unit ex205 during shooting by the camera unit ex203 to
the multiplex/demultiplex unit ex308 as digital voice data via the
voice processing unit ex305.
The multiplex/demultiplex unit ex308 multiplexes the coded picture
data supplied from the picture coding unit ex312 and the voice data
supplied from the voice processing unit ex305 by a predetermined
method, the modem circuit unit ex306 performs spread spectrum
processing on the multiplexed data obtained as a result of the
multiplexing, and the send/receive circuit unit ex301 performs
digital-to-analog conversion and frequency transform on the data
for transmitting via the antenna ex201.
As for receiving data of a moving picture file which is linked to a
Web page or the like in data communication mode, the modem circuit
unit ex306 performs inverse spread spectrum processing of the
signal received from the base station ex110 via the antenna ex201,
and sends out the multiplexed data obtained as a result of the
processing to the multiplex/demultiplex unit ex308.
In order to decode the multiplexed data received via the antenna
ex201, the multiplex/demultiplex unit ex308 separates the
multiplexed data into a coded bit stream of picture data and a
coded bit stream of voice data, and supplies the coded picture data
to the picture decoding unit ex309 and the voice data to the voice
processing unit ex305 respectively via the synchronous bus
ex313.
Next, the picture decoding unit ex309, which includes the picture
decoding apparatus as explained in the present invention, decodes
the coded bit stream of picture data by the decoding method
corresponding to the coding method as shown in the above-mentioned
embodiments so as to generate reproduced moving picture data, and
supplies this data to the display unit ex202 via the LCD control
unit ex302, and thus moving picture data included in a moving
picture file linked to a Web page, for instance, is displayed. At
the same time, the voice processing unit ex305 converts the voice
data into analog voice data, and then supplies this data to the
voice output unit ex208, and thus voice data included in a moving
picture file linked to a Web page, for instance, is reproduced.
The present invention is not limited to the above-mentioned system,
and at least either the picture coding apparatus or the picture
decoding apparatus in the above-mentioned embodiments can be
incorporated into a system for digital broadcasting as shown in
FIG. 29. Such ground-based or satellite digital broadcasting has
been in the news lately. More specifically, a coded bit stream of
video information is transmitted from a broadcast station ex409 to
a communication or broadcasting satellite ex410 via radio waves.
Upon receipt of it, the broadcasting satellite ex410 transmits
radio waves for broadcasting, a home-use antenna ex406 with a
satellite broadcast reception function receives the radio waves,
and a television (receiver) ex401 or a set top box (STB) ex407
decodes the coded bit stream for reproduction.
The picture decoding apparatus as shown in the above-mentioned
embodiments can be implemented in the reproduction apparatus ex403
for reading off and decoding the coded bit stream recorded on a
storage medium ex402 that is a recording medium such as a CD and
DVD. In this case, the reproduced video signals are displayed on a
monitor ex404. It is also conceived to implement the picture
decoding apparatus in the set top box ex407 connected to a cable
ex405 for a cable television or the antenna ex406 for satellite
and/or ground-based broadcasting so as to reproduce them on a
monitor ex408 of the television ex401. The picture decoding
apparatus may be incorporated into the television, not in the set
top box. Or, a car ex412 having an antenna ex411 can receive
signals from the satellite ex410, the base station ex107 or the
like for reproducing moving pictures on a display device such as a
car navigation system ex413.
Furthermore, the picture coding apparatus as shown in the
above-mentioned embodiments can code picture signals for recording
on a recording medium. As a concrete example, there is a recorder
ex420 such as a DVD recorder for recording picture signals on a DVD
disc ex421 and a disk recorder for recording them on a hard disk.
They can also be recorded on an SD card ex422. If the recorder
ex420 includes the picture decoding apparatus as shown in the
above-mentioned embodiments, the picture signals recorded on the
DVD disc ex421 or the SD card ex422 can be reproduced for display
on the monitor ex408.
As the structure of the car navigation system ex413, the structure
without the camera unit ex203, the camera interface unit ex303 and
the picture coding unit ex312, out of the units shown in FIG. 28,
can be conceived. The same applies to the computer ex111, the
television (receiver) ex401 and others.
In addition, three types of implementations can be conceived for a
terminal such as the above-mentioned mobile phone ex114: a
sending/receiving terminal including both an encoder and a decoder;
a sending terminal including an encoder only; and a receiving
terminal including a decoder only.
As described above, it is possible to use the moving picture coding
method or the moving picture decoding method in the above-mentioned
embodiments in any of the above-mentioned apparatuses and systems,
and using this method, the effects described in the above
embodiments can be obtained.
INDUSTRIAL APPLICABILITY
The present invention is suitable for a picture coding apparatus
for performing inter-picture coding to generate a predictive image
by generating commands indicating correspondence between picture
numbers and reference indices for designating reference pictures
and coefficients used for generation of predictive images,
designating a reference picture to be referred to using a reference
index, when performing motion compensation on a block in a current
picture to be coded, and performing linear prediction using a
coefficient corresponding to the reference index on a block
obtained by motion estimation in the designated reference picture.
In addition, the present invention is suitable for a picture
decoding apparatus for decoding a coded signal obtained as a result
of the coding by the picture coding apparatus.
* * * * *